How/when do babies sit up?

Sam hasn't got much balance and can only sit unsupported for a couple of minutes at the most before he flings himself sideways or backwards. My friend's baby is two weeks older than Sam and has always been an awesome sitter upper! She doesn't fall over at all and has been doing this since about 4 months! Sam however is rolling all over the place, non stop and he backwards shuffles on his head and feet to get where he wants to go. He can't pull himself from the crawling to sitting position yet, but all babies are different and they reach all the milestones eventually, even back to front sometimes!

Lucas was able to sit up whilst supported with his breastfeeding (small tri-pillow) pillow since he was 2-3 months old, and then around 5-6 months I could place him in the sitting position on the floor with his toys and he could support himself!

Just recently in the past month he has started putting himself into the sitting position whilst he is crawling and rolling around or pulling himself up and walking along furniture/cot sides etc! He just started doing all these things in the last two weeks really ....quite scary how one day they are totally mobile...seriously just happened overnight. Now there's no stopping him!

In short, enjoy your bubs while you can and make the most of every moment with them, they grow so fast :(

I think 6 months is the general age for when most of them start to show signs of, or start sitting up without support! (say if you place them on ground like that).Some babies crawl first and put themselves to sitting position.

My boy did it opposite way and only started crawling properly on all fours yesterday. every bubs diff and thats what makes them so unique and beautiful each in their own way

Sorry for waffling on here, a bit bored at the mo haha