You shouldn't have to prune a young Japanese maple unless you are trying to change its form in some way. Sometimes a young maple will send out an especially vigorous shoot that you might want to prune to keep the tree in balance. Other times, a young tree might tend to grow too much to one side, and you might want to correct for that. Most of my young maples I just leave them alone and let them do their own thing, except I do often stake them so they will grow somewhat upright as many maples tend to spread.

Thanks

I was referring to seedlings. There was a guy whose post I was reading that said to hard prune young trees to make them fuller. Is that correct????

Here is a link that might be useful: Maple Pruning Tips

dawgie is correct you will not need to prune them unless you enjoy doing so ...and only in the mid summer or fall period when they are NOT growing ...seedling or grafted it is NOT necessary they will "fill out" on their own and don't see how trimming will speed this up or why you'd want to unless as I said your a topiary sort of person or as was said... the tree is extreemly mis-shapen!!! I second dawgie's advise and don't understand your additional question...I think he answered it as far as i can see... David