I think that the first 3 are the hardest and then gets easier from there. You have already done the ground work with the older kids so from number four they are growing up with the rules already set! A friend always said that 4 was the minimun number of kids to have as 1 is alone, 2 only have each other and fight, 3 there is always the odd one out but 4 just works great! I know this is just her opinion but I see her sense!