Although he absolutely hates it, we started tummy time pretty early in D's life. At 3 weeks of age, he couldn't life his head up, but he sure knew how to get those little legs underneath him!
Since then, D has developed more neck strength and I swear, if this child could crawl with his head on the ground he would right now! Now, I haven't been around an infant in a VERY long time, but I don't think I've ever noticed a little one trying so hard to push up on their knees before effectively holding their head up! Since he's discovered how to use his legs to move, D has mastered the art of moving around in a circle simply by lifting up (while on his back) with his feet and successfully moving a few inches in a clockwise fashion. More times than not, I find him in the opposite direction than how I placed him. Well, with all that leg strength, we are close to rolling over! Laying on his play mat on his side has now become a favorite activity! I think corralling D is in our very near future!