I wanted to give an update to this thread for any other parent wondering. My son did the time trial... it was a 10k(6.2 miles). He finished with a 16.5mph average speed. He was 27seconds behind the winner. Wind was a factor , but I think my son did pretty good.
The next training ride after the race was significantly higher in avg mph than what we normally do(13+ normally, this was 14.5 +). Lol my son dropped my fat ass on that ride. I was thinking, what the hell? Where did this speed come from?
He is signed up for more races this summer. Both mtn and road. We shall see.
I think he has a long way to go, but he is getting stronger every ride and I am proud of him.