Can someone please answer me, what is with the age ratings on kids' toothbrushes?? I was picking out Eli a new one today because his was all "hairy" (AKA the bristles were really frizzled. hmm, I like that word, I think I just made it up) and looking at all the brushes on the shelves they all look the same to me. I select one that I think looks good, then flip it over and it says 5-7 yrs! So I put it back and kept looking. There's Stage 1 and Stage 2 and maybe Stage 3 or whatever, but what's the difference in these brushes? And does it really matter what I use when??