Being in childcare I had to find a way to get toddies to pick up. I found if your specific with what u want picked up they usually will do. For example don't just say "go and clean up your toys" direct more with "please pick up your buzz lightyear" and do it with them all till they get the point. If its a big activity like puzzles or Lego, set the example and start picking it up and ask them to come and help you. If none of that works turn it into a game of some sort. Main advice is to stay away from "clean up you toys". It's to overwhelming and the kids don't know where to start at that age so they just avoid and don't do it.