Is it time to put a small litter tray in their room? Also, when should I start to introduce wet food or even dry food? I'm new to this baby kitten stuff.
Yes, give them a shallow cake pan (aluminum) to use with a little litter. They may not use it right away but will get the idea soon.
Feeding solids if they are nursing well, should be about 5-6 weeks old - before that, they really are not interested. Mushy canned food is best to start.