What's the difference between a play gym and a foam play mat?

A play gym is an activity center with an arch and hanging toys designed to entertain a baby during tummy time and back play, typically from newborn to around 9-12 months. A foam play mat is a large, thick padded surface meant for crawling, rolling, and protecting babies from hard floors, and it stays useful well into toddlerhood. Many families end up owning both.