Not an expert but from what I have read the seedling will first start to sprout leaves that only have one finger instead of the 5 or 7 fingers on normal adult leaves. Next it grows another node with maybe 3 finger leaves and so on until finally the new nodes will have 5 or 7 finger leaves, maybe even 9 sometimes 11. When the new nodes aren't adding any more fingers then it is usually considered to have made the transition fron seedling to vegitative stage.