I have had issues with GK too on my 18 month old. They just don't last and they leak out the sides of the legs as they are really wide in the crotch so the insert folds up and leaves the outer cover exposed. Try what the others have suggested! Also I fold up another bamboo booster (tri-folded) inside the pocket but it does make it bulky. But I can get over an hour with just the one bamboo insert that you buy with it. They just don't suit my DD is the long and the short of it.
ETA- I just buy one or two of a nappy until I see that it is a good fit and size on DD before buying any more...