Full contact sports should be adapted to children to have no full contact. If it’s not the case, the teachers are morons, dangerous and probably criminals, and you should obviously not leave your kids there.
In fact, regarding full contact combat sports, even for adults training does not involve full contact to the head in most cases, only competitions and examinations may. There’s a lot of choice of schools and rulesets, so adults can choose whatever level of contact they are comfortable with.