What time is your lunch and nap times? They may need a bit of a bigger snack, or lunch moved up earlier so that thety are not so starved come lunch time... I usually serve a small snack around 9:30-10am and I serve lunch anywhere between 11:30 and 12:00 and give them about 30 mins to eat before I start getting them down.
I used to get them all changed and ready to nap RIGHT after lunch, but found it left no time for me during my break to tidy up etc.
Now I have them play for 25-30 mins while I do the dishes, clean the table, sweep the floors. So when they are all in their beds, I can actually put my feet up and do NOTHING!! haha!