My 6.5 month old has never liked tummy time and I assumed he would grow to like it as time passed. He has been able to roll from tummy to back for a few months, but still has not rolled from back to tummy. When I place him on his tummy he does not seem to be able to arch his back and really get his head up, which I am sure would make him happier. He is able to sit unassisted and reaches for things at a distance so he seems to have pretty good head and abdominal strength. Any suggestions? The mama worrier in me is really getting going about this...