Well, since I'm currently transitioning a 1 year old baby I'm not too fond of that age group right now. Just kidding, but I wish he would settle down. I find that all my dckids start out at 1 year old or under since that's when the mat leave Moms return to work in our area. I do like to start children early so that they learn my rules as they learn everything. By the time they are 3 or 4 they have been here for a long time usually and are wonderful.
Sure they go through lots of phases and try to push their boundaries now and then, but I haven't had major problems. My Jeckyll/Hyde boy was a real test but he was good for me and a monster in front of his parents. Then I had a girl who was a super tattletale but I would tell her to talk to her friends instead of me about 50 times a day and we made it through. They were the worse ones.
Thankfully, I don't have school aged children in my daycare because I would NOT want to have children of that age here. I do have a 4 1/2 year old girl here every other day because she just started JK but she's been here almost 4 years already and knows what I expect from her and is a real gem.