What do you need in terms of electronics? An R/C system with electronic speed control and a servo for the steering? Not sure it would be worth developing that from scratch. You would probably be better off teaming up with an established toy manufacturer. The certification cost for R/C equipment can be high. If you just need electronics for a working prototype, I would suggest you buy a R/C car of suitable size from one of the Chinese online merchants and use the equipment from that. Can’t help with electronics design but I have over 30 years experience with R/C equipment so let me know if I can be of any help with that.