It is an oath, not a contract.
Boy Scout & Girl Scout clubs also speak oaths, which in some cases, is enforced punitively.
Children have also spoken oaths in secular courts under the penalty law.
Society, in general, rarely objects to children commiting to an oath.
WT will continue to exploit this as long as secular governments tolerate it; and even if religious protections were revoked, WT would probably defy as part of "theocratic warfare"
Like the old hypocritical preachers said: "Religion is a snare and a racket!"