DS is 20 months and currently in a nanny share with one other child his age. Their nanny takes them to play groups/parks most days and they seem happy and well stimulated although there are days when they can't go out due to the weather and DS starts to climb the walls. He has loads of energy and is very curious/keen to learn so I was wondering when the ideal time was to start introducing more formal learning, numbers/colours etc. I do all of this with him of course and he is starting to know colours but I am wondering if he would benefit from a few days in a nursery environment when there is a more formal program. Or is it too early and he has enough stimulation through just play?