The best time to add bleach is in the evening when the sun is off the pool. In that way, all the chlorine can go to oxidizing the goo in the water and none of it will be lost to the sun. However, it is also ok to add it at other times. Especially when a pool is fighting algae, or has a high chlorine demand for some reason, etc.

Keep your chlorine between 5-10ppm. Your grandchildren are perfectly safe when swimming with chlorine at those levels with a CYA of 70ish. (Actually, it is also fine to swim when chlorine is at shock level but you probably would want to wear an old swimsuit if you did so.) People are often afraid that a chlorine level of 5-10ppm is too harsh; but the fact is that with a CYA of 70, chlorine is no harsher at 5-10ppm than it is at 1-3ppm with no CYA.