Our scheduled rest time is for two hours here also. Imo the three year old needs at least that depending on what he/she sleeps at night. The six year old if here would lay down for a quiet time at the same time and if he/she falls asleep then he/she needs the sleep, if not then he/she would be up after a 30 minute rest and participate in a quiet activity until the others wake.
Here is the recommendation from the CDC:
http://www.cdc.gov/Features/Sleep/