infant development

I’m Mahee, I have a 3 month old son. I need help for my son’s development.

  • he hasn’t yet roll over completely. But he can do side to side. How should I train him to do it completely?. If I put him down on his back, he will start to play.
  • for crawling, since he is suffering from eczema (dry & sensitive skin), we could not put him on the crawling track( made with vinyl base). But he enjoys to look around when he was on his tummy( we use bedsheets for tummy time).
  • for knowledge development, I have to make flash cards. I have some pics of animals, birds, veggies and fruits. For his age, Is this enough? Or Should I make/show more with countries , flags now?.
  • during playtime, do I have to switch toys each time, like 2 or 3 at a time? Or same all toys each time.
    All suggestions are welcome. Thanks.