I have a very active six month old son. He is just learning to sit up, and the past few weeks has become very fussy--I think he has figured out that there are lots of things to do, but he is not mobile enough to do them. I just finished reading Burton White's book "The First Three Years," in which he recommends a johnny jump up toy that is suspended in a doorway, to be used in moderation and barefoot, to help quell "overuse of the demand cry". So far my son loves it; we play disco type music and he bounces and twirls, while I get a 15-20 minute interval to use the computer and keep an eye on him. I've been using it twice a day. I mentioned it to several moms I know and was told that this type of toy is not suitable for kids because it does not develop the correct leg/hip muscles, and may end up delaying him walking. I only intend to use it for another couple months until he learns to crawl, plus it has a 24 lb. weight limit and he weighs 18 lbs. now. What do you think of these devices--will it hurt him or impede his walking? John has quoted Burton White's book, so I respect his recommendations. The revision date on the book was 1995, so maybe there was research done after that printing about these toys?