Do babies only sits up from tummy position when they start crawling? If not when will they start doing that? In addition, will propping up a cushion below the tummy helps them to crawl ?

Babies all have different milestones. My no1 sat before he crawled. No2 and 3 crawled before they sat. Many children also skip crawling and go straight to walking. Here's what i did to encourage my kids to crawl. I put them on their tummy daily. I will also lie on my tummy to play with them. When I'm not lying down I will put a toy for them to reach - usually it's a ball because I like how when their hands reach the ball - the ball will move further and it encourages them to continue inching forward. Hope this helps!