Play stupid games, win stupid prizes.
Fleeing an officer in the middle of him writing a ticket, then trying to walk off when he is preparing to cuff and detain you for said act, then having your son try to attack the officer for what appears to be a second time in the same event and then fleeing again... Not surprising that the backup would overreact a bit. I will not defend firing on children, but the mother and son did contribute quite a bit to escalating the situation.
Bottom line; don't flee/resist a lawful detainment/arrest.