B.T.
Wow. My kids are 5 and 7 - the 5 yr old was just ready to sleep over at other homes about 6 months ago. Now it is great and they both do sleep overs together here and at neighbors. I would never have done it before 4 yrs though. I've had 5 and 6 yr olds fine the entire night until bedtime and they start crying and I've had to call parents. Would never even think about younger kids - you are super brave to even consider it :) If you have cousins, that might be a good starter.