To prevent SIDs, pediatricians recommend that babies put down to sleep on their backs, and only their backs -- no more side-sleeping, you people with babies just a few years older than mine! And heaven forbid, no sleeping on the stomach, as babies did forever, before "side or back" became the recommendation.

So babies nowadays spend an awful lot of time on their backs. To strengthen their neck and other muscles (and prevent flat heads, which my mother is very worried about) pediatricians also recommend a few minutes of "tummy time" every day.

Tummy time, week 6: Baby lies with his face planted in the mat, sobbing.

Tummy time, week 10: Baby struggles to lift his oversize head off the mat for a few minutes. It sinks back down. He starts to sob.

Tummy time, week 12: Baby can actually hold head off mat for minutes at a time, grunting but not sobbing, and look around a little.

Tummy time, week 16: Tummy time is no longer enforceable, since baby has mastered rolling onto his back.