Oh, I get the 'full of beans' idea, Grinity! My son is regularly full of beans, although at age 8, he is starting to outgrow it and be more focused and calm. <at least at times I hope he outgrows it!> I would interpret it as when they are just too full of gas/energy. I think it is just one component of the overexcitabilites that gifted kids can have.
Pinklady: Sometimes these kids just need so much stimulation, that if they are not receiving it in some form or another, then they create it themselves! Their minds just need to whirl and dance and play. It is a challenge to get them to do it in appropriate ways (reading exciting books or experimenting with an explosive chemistry set!) verses other rather inappropriate ways. Does that sound like your kids? Maybe not?
<note: Because I have a science background, I see nothing at all wrong with things that go boom!>
