I bought these for my son about 2-3 years ago when he was around the age of 3. I liked the idea that they would grow with him and hopefully he would learn how to inline skate pretty well. They adjust with the child, the size of them and the style of the wheels. The kids wear shoes underneath them which is my only complaint, at almost 5 now and wearing a size 10 toddler shoe it is hard to get them on with any shoe, he will wear them with just socks but I cannot imagine that they are comfortable, he does not complain though. When he was little the shoes did go in pretty easy.
They are made of plastic and it seems like a cheap plastic but we have had no problems with them, although he is not rough and doesn't use them alot. He does enjoy them but gets frustrated that he cannot skate well. You can have all the wheels in the locked position, or just locked so the back one won't reverse or all of them free moving. He likes the back one locked, which is especially good for going up hills. To start a child it is nice that they all lock.
I really like these and for the price I paid, I got them 50% off, they were quite a deal.