my son was 3 months when he could sit up he has no problem he can pull up and stand but he's crawling on his belly and he'll be 8 months sunday

my youngest started sitting on her own at 5 months she's 6 months now and she's not quite crawling but she can go in circles in her belly.

Sit up at 6 months. She is 7 months and still not crawling yet.