This means to have loads of energy. It is a polite way of saying that a child is a maniac. I was often described as being full of beans as a kid and now it is my wife's way of telling me to keep still when she is trying to get to sleep. Strangely the same expression in some parts of the US means that you are exaggerating or talking bollocks! Found on https://www.encyclo.co.uk/local/22179