my baby was 2 months and still in newborns. she only recently went up. she's tiny, though. you'll know when it's time. my girl had a huge blow out and I knew it was time to move up

It's by weight. My little man has issues with his weight so he was in newborn until almost 3 months. Then went from size 1 to size 3 by 5 months. All depends on the baby I've noticed

She came out wearing size 1. 😂 but don't stress it. As long as your doctor isn't worried, you shouldn't either! :)

I just went by the weight on the box!

My little cub stated size 1 at 2.5 weeks. She is now almost in size 2 and will be 2 months old on Sunday. It all depends on the weight I think.