I bought this for my 3.5 year old and she LOVES it!  She runs a little below average on height, so the bag looks just a touch big on her.  She can put it on and take it off easily and without help.  The water bottle pocket on the side is great to have.  We've tried a big Camelbak bottle and a smaller Playtex water bottle in the pocket and they both fit.  The zippers have pulls, so it's easy for little fingers to grasp and pull.  My 6 year old liked her sister's backpack so much, so asked for one for herself.  It fits her perfectly.  Average size folders and composition books fit in the pack with no problem.  There's plenty of room for her lunchbox, too.