A minor child cannot relinquish U.S. citizenship and they cannot have it relinquished by someone on their behalf.Not true. You're confusing a situation where a minor is still living in the U.S.A with a minor who has permanently moved to a country outside of the U.S.A. It's xenophobic to assume a U.S. citizen would never renounce their citizenship to become a citizen of the country they are living in. Minors have as much right to pursue citizenship outside of the U.S. as an adult.
A U.S. citizen can renounce their citizenship in favor of citizenship in another country. But they can only do it as an adult. They cannot do it as a minor. Link.
“Parents cannot renounce U.S. citizenship on behalf of their minor children. Before an oath of renunciation will be administered under Section 349(a)(5) of the INA, a person under the age of eighteen must convince a U.S. diplomatic or consular officer that he/she fully understands the nature and consequences of the oath of renunciation, is not subject to duress or undue influence, and is voluntarily seeking to renounce his/her U.S. citizenship.”