There are lots of "ifs:
If the police decide to take action and if they decide that a caution is not appropriate they will refer it to the CPS.
If the CPS decide that a there is sufficient evidence to support a reasonable chance of a conviction and it is in the public interest to proceed) they will take the matter to court.
If he is convicted (either by pleading guilty or being found guilty following a trial) then the matter will be dealt with by way of a "Referral Order":
https://www.gov.uk/government/publications/young-offenders-referral-orders
The Youth Court has no other alternative disposal for the matter. Bear in mind that if court action does result that you or your son may not observe the proceedings. Youth Courts are held behind closed doors. You will be entitled to be informed of the outcome.