It's National Siblings Day! Here's what you need to know

Photos: Kids meeting their baby siblings
Hello, baby! – CNN invited readers last year to share photos of children with their new siblings. Here, Cecelia, 2, meets baby Sullivan. "Cece is very possessive of her little brother. 'He's mine' or 'my brother' or 'my Sully' are her favorite things to say to strangers when we are out together in public." -- Cary Chadwick, Higganum, Connecticut
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Photos: Kids meeting their baby siblings
Jack, 2, and baby Nora – "This was my husband's first day back at work and my first day alone with two babies under 2. Overwhelmed didn't even begin to describe how I was feeling. It was 2 p.m. and I was finally getting around to brushing my teeth, so I laid Nora in my bed. When I came out of the bathroom, Jack had climbed up into the bed with her." -- Emily Thomas, Marietta, Georgia
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Photos: Kids meeting their baby siblings
Abigail, 11 months, meets baby Caroline – "We worried that since the first one was still basically a baby herself, she'd be jealous about the new baby crowding her turf. Luckily, they've been best buds since their first meeting." -- Andrea Jones, Atlanta, Georgia
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Photos: Kids meeting their baby siblings
Mikey, 17 months, and baby Emma – "My wife and I were worried how he would react to having a baby sister. We had our baby girl Emma on February 28. She is beautiful, but is a little colicky. The first thing my son did when we came home was put his hands out to hold her." -- Michael Galarza, Staten Island, New York
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Photos: Kids meeting their baby siblings
Julia, 17 months, meets baby Willy – "My son had been born at home at 4 a.m. while Julia was sleeping in the front bedroom. My husband brought her in when she woke up and she immediately kissed her baby brother. ... Then she couldn't stop staring in amazement at him." -- Jennifer Prescott, Tustin, California
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Photos: Kids meeting their baby siblings
Tennyson, 18 months, meets baby Marlowe – "Our oldest daughter was less than thrilled when meeting her baby sister for the first time. ... I can only imagine what was going through Tenny's mind." -- Andrea Brown, Tulsa, Oklahoma
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Photos: Kids meeting their baby siblings
Hudson, 2½, and baby Brody – "The first few days he would cry and scream, 'I don't want Mommy to hold baby Brody!' He still has his moments, but he's accepted that Brody is sticking around." -- Sarah Hager, Louisville, Kentucky