I guess so....I think they are illegal here too meanwhile but i live in a small town and know all of the policemen her personally, so they do not bother stopping me. According to german regulations the bike is not street legal at all, lacking front, back and wheel reflectors and using a non approved lighting system. But would you put those kind of things on a bike like this?
I see those kid's saddles all the time mostly on oldtimer car swap meets. Usually I do not have to pay much these. The one on the bike is the only one i found in leather, all the others are made of plastic (rubberlike). I did not find the foot suppports yet. If you are interested drop me a line and I will see what i can find.