Dear Beth G.,
Your expectations are too high for children who are so young. While children of such a young age are certainly capable of picking up after themselves, with our supervision, after play, they are not capable of handling this task on a regular basis by themselves.
You would probably be better off having the children in separate rooms at their age. They don't yet have the cognitive capacity to do what you're expecting.
So, you're frustrating yourselves and punishing your children when there is no need to do either. Try to change your expectations and you'll be better off. Remember, the kids should be picking up after themselves, within reason, but they'll need your gentle reminders and supervision.
Make a game out of it. Set the timer for 15 mintues and if they have finished in 15 minutes they can have a popsicle or something.