My baby boy is 10 months old this week and isn't yet crawling. He has just figured out commando crawling but just can't figure out how to move his legs properly to actually crawl. He has no interest in walking, pulling himself up or cruising. I know all babies develop at there own pace but I can't help but worry when I see all the other babies his age doing all of these things. Is there anything I can do to encourage crawling or walking? He spends a lot of his day on his tummy already. At what stage do I start to worry he isn't reaching these milestones yet?