Every baby's milestone is different . U can make it baby sit by putting pillows on the side . Also some baby's start walking without crawling . So let ur child find his pace . Stimulate the actions but don't force and don't be upset.

<span style="color:#3B5998;"><b><a href="http://app.babychakra.com/article/1821">6 Months Baby: Physical Milestones</a></b></span>

My baby started sitting after seven months and started crawling in 9 months ,every baby is different so let your baby take it's own time to learn

Some babies will miss crawling milestone and directly stand so don't worry. It's just six months, is he able to hold himself for few seconds if you make him to sit?