Powerglide, that could be interesting. Would he be smaller, like I recall his being a minibot in g1. So maybe the tf:prime Arcee size or smaller?
I may pick one of the human kid characters, or make an original one since there are some types of rp that the kids can do that the bots can't, and vice versa. If I did an oc kid character I'd do one closer to Raf's age since it would look odd at school, and other places, a kid hanging out with teens, and 2 teens hanging out with someone so much younger.
Plus I think a kid at school may start noticing things. If you look at the right time and are at the right angle, assuming bumblebee and bulkhead keep their windows dark, and it looks like they don't, you can see as Miko or Raf gets in that there is no driver, if you time it right you could take a picture, and start gathering other evidence. Who is that woman who drives Jack's motorcycle, not jack's mother. her helmet looks totally different then jack's. Why has he not seen her walking away or towards the motorcycle. & other things.