I have been umpiring for 5 years and I can tell you that kids around 7-8 can not throw the ball over the plate. I often times have to expand my strike zone so big just to get the other kids swinging the bat. Kids just like getting on base so if they can walk to do that, that's just what they'll do. I like the idea of pitching machines at this age group as it gives the defense a chance to act out there as more kids actually are swinging the bat.
There are some teams that have some pitchers that can do it, but anymore league baseball has been becoming obsolete anyways. The majority of kids that play ball anymore are playing on tournament teams which is sad because the ordinary kid that just wants to go out and play just doesn't get that chance anymore.