DD started sitting up right when she turned 5 months old, but still doesn't have the best balance. If she has just a little bit of support, she is perfectly fine, otherwise she'll stay balanced for a couple minutes and then topple over. However, she is "army crawling" like a pro! She scoots/slithers all over on her belly - it is adorable! She'll turn 6 months next week.
How about your LOs?

Re: Sitting Up & Army Crawling
That is so true! DS#1 was never swaddled and a belly sleeper from the very beginning. He started rolling at 2 weeks old and did everything super early. At 6 months, he would walk holding onto our hands, at 8 months he was taking steps on his own, and at 10 months he was walking from room to room.
With our DD, we swaddled her up until about 5 months and she really just took off with her rolling.
It's not a big deal...I'm not one to obsess over milestones but it is interesting....I've always wondered if there was some sort of correlation between belly sleepers and unswaddled babies and meeting physical milestones early.
He isn't army crawling yet, but he rolls both ways easily, turns himself in circles on his belly, and sometimes manages to scoot himself forward, although I think that's accidental. We encourage him by putting toys just out of his reach, or putting our hands on his feet so he can push off. He has pulled his knees up under him but that's as far as that went.