My 10 month old sat by himself at about 6 months. As far as crawling. He doesn't and he probably won't. He can roll, scoot backwards and stand up holding onto things, but his daycare provider doesn't believe he'll crawl. Several of my friends and relatives children never crawled either.
My twins were about 1 1/2 years before they could sit without suport or crawl. They were severely delayed. There is occupational and physcial therepy for infants to catch them up to where they should be for their age. If you are concerned talk to your dr and he can get the help started for you.
I have four kids and the earliest to sit up alone was at 5 months and the latest was at 7 months. As far as crawling they ranged from 7 to 9 months. My oldest was walking at 10 months! I wanted to tie her down LOL It is safe to say kids vary GREATLY! The biggest difference I noticed was in potty training. Again my oldest was VERY early(15 months) and another was close to 3 and a half! It is so fun to see how different they are and see them grow and change. Mine are now 13, 11, 9, and 6
I have 3 kids my youngest sat at 5 1/2 months and she just started carwling on Arp. 4th....my oldest did things a little late exept sitting she could sit by 4 months but everything she did besides that was late but when she did do it she was a pro I remember making her cereal and she just started rolling past me in the kitchen when she never rolled before and she got things will fast and my son never bothered he had everyone doing everything for him so y move so he was real late with everything he was 18 months old when he started to walk and my youngest well she is practicing her crawling still not great but getting there
well autumn just began sitting on her own 2 days ago (she is still a day shy of 6 months) but i have to sit with her because she will throw herself back and hit her head on the floor (jeez!) but she can sit for a long period of time...it is just amazing to me because one day a baby cant do something and then 24 hrs later they can....wow and what is even more astounding is they have no idea they are meeting a milestone...they just do it.
My first child was sitting unassisted at 6 month, my second child at 7 months, and my twins at 8 months.
My first child never crawled, but went right to walking at 10 months, my second child started crawling at 10 months and walking at 11. My twins started crawling at 10 months, and started walking just a little while ago, at 13 months.
Just goes to show you all kids are diffrent!! Oh, and instead of just running down the list of "my kids" , my oldest is Brenna, and shes 7, Noah is my only son, and hes 3, and my identical twin girls, Amie and Abbie are 14 months, almost.