Commando/crawling before sitting

[luna moth]

Gymbaroo ladies certainly thinkt hey are an authority on human movement- lol! I used to work with a particularly militant one "NO, Jayden, your fingers have to face INWARDS!" (She was actually very lovely.)
[/hijack]

It's actually very common that babies crawl before they can sit - they're using different muscle groups. Lots of crawling will help them to work on core strength, which will help them to sit up. In theory. In practice, there are plenty of babies who don't want to sit still, so they don't bother!