I used to put my first five babies down on their play mats very soon after they came home from hospital, and they loved it.

My last baby was born almost 3 months prematurely though, and has a huge 'lump' on his eyelid, something called a 'haemangioma' = some sort of birth mark.

While medics all advice that this 'lump' will disappear in time, at the moment its still growing.......ds is now 17 months old.

We have only put him on his playmat on the floor in last few months, as we felt he would 'bump' his head and were worried in case his older siblings hurt him accidentally etc. The result being that he just won't stay on his mat, its as if he's petrified, he trembles like mad and screams the house down.
So naturally we don't leave him there, we pick him up every time...which means that he is not even crawling yet. Surely its better for his crawling/walking to be delayed than for us to risk his 'lump' bursting though.
Sorry for rambling, just got carried away.