They don't need too much to stimulate them.... but there definitely sounds as though there is no structure at all.
When I worked in childcare, with that age group, we had 4 tables, and 2 mats.
At each table there was an activity - building blocks, drawing or painting, playdoh with (something - ie toy cars), puzzles.
On the mats there was an activity - dress ups on one, reading books on another (usually things where they can spread out).
This is where its your job as the responsible person to start structuring these kids to play and focus on one thing for a while. let them choose one by one a table or mat they want to play at. Then after an amount of time allow them to swap or move to another table/activity. It is the best way to get them started in preparing for a more structired routine as when they move up levels, they are expected to sit at one activity for much longer periods of time.
If they are acting the way they are, you need to stop the activities. Take them away from them, sit them on a mat and calm them down. Tell them when they're quiet they can play again... regroup them, refocus them.