I had an old long track phazer that I used as a between sled for my daughter. I was worried about the jam - but I couldn't find a decnet 380 for her to take up to the mtns with me.
One trick I tried was putting some dense cell foam under the throttle (glued it in). She could only push it in so far no matter how hard she pushed, but I could get it wide open if I had to get it unstuck, etc.. As she was getting braver and handling the sled better, I changes the foam out to something more pliable. It wasn't until my daughter was 10 that I trusted her without it, cause those 485's are pretty peppy for a kid.
Nice think about the Phazers vs a 380 or 340 is getting the 136 skid stock. The downside is I could not find an electric start kit for it.
I just found and old 380 MXZ that I am going to mod for the 5 year old - 136" track, etc. That should make a great starter machine for him. Absolute best thing about it is the RER reverse. Don't realize how much you miss it until you don't have it anymore.