They do use the same rims, on Tower they have the same part no. in the parts listing.
Grasshopper
http://www2.towerhobbies.com/cgi-bin...=TAMC0356&P=PU
Hornet
http://www2.towerhobbies.com/cgi-bin...=TAMC0346&P=PU
Probably the hardest part your nephew will have is painting the body, make sure you tell him about multiple thin layers and waiting for it to cure i would think.