This may sound crazy but do you have space for one more 4-5 year old boy .... Three would take the focus off each other.... Outings to different parks ..... Everyone loves the splash pads around here. In summer I like to do a lot of water and art "messy type " stuff outside many of my little boys loved that kinda stuff. Playing 'car wash' with all our ride on toys was a real favorite. As far as quiet time goes do you allow computer use ? I would let them each have their own time playing educational games each naptime while the other child does another quiet activity. When I had school agers in the summer they could bring their ds or ps2 devices to play at nap time not my favorite but it kept them quiet while the little ones napped.