Many dads asked me how hard my son threw in h.s. I always told them the truth and, of course, they'd come back saying their kid threw that or harder. Of course, I knew it was nonsense.
I don't worry about it anymore because all of those dads and their players have disappeared.
Tell the truth about velocity. You don't want some college or pro scout to show up thinking your son is tossing 89 when he's really at 80. If your son takes a sudden jump thereafter it may be like the boy who cried wolf.