Editor's note: Kelly Wallace is CNN's digital correspondent and editor-at-large covering family, career and life. She is a mom of two. Read her other columns and follow her reports at CNN Parents and on Twitter.
(CNN) -- For several weeks, Frances Johnson had been telling her 2-year-old son Noah the following: "Mommy and Daddy are going to go to work for a while ... but we always come back for you.
"We always come back for you."
Noah is too young to understand that his mommy and daddy's "work" involves deploying to Afghanistan just around the new year, and that "a while" could be between six and 12 months. But there are signs he seems to grasp how his life is about to dramatically change, Johnson said.
When she said goodbye to him at the airport, which would be the last time she'd see him in person for months, he wanted to come along and said, "Me mama work?"
Johnson, who didn't want to cry in front of Noah for fear of making it even harder on him, couldn't hold back the tears.
"I started crying and told him that I wish he could come to work with me, but that I would come back to him like I always do as soon as I could."
"I said, 'I always come back for you.'"
Then, fearing she was really going to lose it, she gave him lots of kisses, hugged him for a "very long time" and walked away as fast as she could.
"It's really rough, I'm not gonna lie," she said in those first days after their goodbye.
I can't even imagine how rough. The most I've been away from my girls, ages 6 and 7, was 2½ weeks.
The only people who perhaps can truly understand how rough it will be are the small group of military couples who have been deployed at the same time.
From 2011 to the present, 681 Marine Corps couples had simultaneous deployments, according to the Manpower Management Information Systems Division Headquarters for the U.S. Marine Corps.
'Man, this is going to be hard'
The Marine Corps did not order the Johnsons to deploy together. Frances Johnson, a Marine Corps combat correspondent, volunteered with her husband's full support because she has not deployed to Iraq or Afghanistan during her six years in the military and always wanted to experience a deployment.
Her husband's enlistment was about to end after 10 years, so he would remain home with Noah while she deployed. But then her husband, a Marine sergeant who is a program manager with infantry detection dogs and a clerk with the Anti-Terrorism/Force Protection unit, was offered a deployment that would give him a chance for a promotion to staff sergeant.
Johnson encouraged her husband, Andrew, whom she calls Drew, to take it, even though it would mean both would be away from Noah at the same time.
"He's always been there for me. He's always encouraged me to do more and grow," she said. "I said this is kind of a sign. 'Hey, it's not time for you to go just yet. You still have a little more work in the Marine Corps.'"
Since making that decision, they have tried not to dwell on how tough it will be for Noah and for them, but of course, that is much easier said than done.
"I said, 'At least we'll be together,'" said Johnson, who will be deployed to the same base as her husband in southwestern Afghanistan. "Other than that, it was just a whole lot of, 'Man, this is going to be hard,' especially when (Noah would) come into bed with us in the morning. He's still sleepy but he climbs on in and he's just all happy and cuddly and it's just, 'Man, I'm really going to ... this is going to suck.'"
'I've heard that I'm a bad mom ... for leaving'
Her mom and dad, who live outside Denver, agreed to watch Noah while she and her husband are overseas, so they moved him from California to Colorado shortly before Thanksgiving to help him adjust to a new routine. She then had to return to work in San Diego in early December, and her husband a few weeks later.
They'll be spending Christmas away from Noah before departing to Afghanistan.
Johnson's family has been extremely supportive, but not everyone understands their decision, especially since it was their choice.
"I've heard that I'm a bad mom and a bad wife for leaving, especially when we didn't know Drew was going to be going. I heard a lot of, 'How could you leave your son like that?'" she said.
"Sometimes, people who find out that both of us are deploying, they kind of say backhanded comments like, 'Wow, you guys are so brave for leaving your son. I could never do that.' And, 'You know, I try to be so centered around my kids.' And it's like, 'OK, well, me, too, but this is my job.'"
It's hard to know if those same people who seem to be passing judgment, even if they are doing it in a less than direct way, would have been more understanding a few years ago when there were two wars going on at the same time, the conflicts in Iraq and Afghanistan, and both were getting more attention here at home.
But regardless of the answer to that question, the fact that some people don't seem to appreciate Frances and Drew's service and the extraordinary sacrifice they will be making isn't lost on them, especially on Frances.
"It hurts, but my husband is very, very good about focusing on the positives, because I am very good at focusing on the negatives," she said with a laugh, remembering a wacky time recently when Noah was cracking up during a family silly string fight.
"After everything had kind of settled down, (Drew) was like, 'See he's going to remember the good times and he thinks, this is good, and he's not going to say, 'Well, I can't believe you left me when I was 2. He's going to remember the good.'"
'He can still have me close'
Frances plans to take "quite a few pictures" of Noah with her along with all the pictures she already has on her iPhone. Plus, she's bringing a special bear she and Drew got when she was 22 weeks pregnant with Noah.
"We had gone to a 3-D ultrasound place, and they recorded his heartbeat and put it inside the bear so I'll be taking that with me," she said.
She and Drew are also leaving plenty behind for Noah, including their bed and some of their clothes so that he can just "hang out with mom and dad's scent."
They've been taking pictures of just about everything they do so Noah will have them on the computer. Her mom also plans to have some pictures printed on little pillowcases and to hang a canvas of pictures in his room.
"I (plan) on writing him because he's very, very smart," she said. "He likes to be read to, so I wanted to write him letters so that my mom can read them to him and he understands that mom's far away but ... he can still have me close."
Leaving a son: 'OK, how do I prepare for that?'
She feels mentally ready for her deployment, especially after a series of classes the military provides to give a better understanding of what she might encounter in Afghanistan. But it's pretty much impossible to know how to prepare for being away from her son, she told me.
"I'm just like, 'OK, how do I prepare for that? How do I?'" she said. "I don't know how to handle that."
She has a friend who has two boys and recently returned from a deployment, and plans to reach out to get an understanding of how she coped with being apart. Still, she continues to have moments where she wonders if she'll really be able to do this. It was especially hard after some recent family outings to the park and SeaWorld.
"Then it's like, 'Man, how can I leave this?'" she said. A few minutes later, she said, the doubts go away.
"We're going to do this and we know it's not going to be that bad and we'll all be better for it,'" she said.
She and Drew, who has been to Iraq twice, are aware of the dangers, but try not to dwell on them. Instead, they focus on the future, especially their homecoming.
"All I can think about is coming back and seeing him at the airport when I fly back," she said. "I keep thinking about how I'll try to be as polite as possible, but I'll probably be running people over just to get to him."
And who could blame her?