Nothing happens to the minor. The recipient does not get in trouble because the minor did not read the assertions, they might get in trouble if the contributor is not allowed to make said contribution, for example "is a foreign national". There are certain steps to take if a contribution is questionable, for example refund it or ascertain that the contribution is legal. Since the question asks the pertinent questions, the contributions is not questionable, unless some other direct evidence is brought to the attention of the committee.
The inclusion of minors in this instance is out of an "abundance of caution". Minors can contribute, but there are restrictions, that
The decision to contribute is made knowingly and voluntarily by the
The funds, goods or services contributed are owned or controlled by
the minor, proceeds from a trust for which he or she is a beneficiary
or funds withdrawn by the minor from a financial account opened and
maintained in his or her name; and
The contribution is not made using funds given to the minor as a gift
for the purpose of making the contribution, and is not in any way
controlled by another individual.
I suppose they feel that it is too risky to accept contributions by minors: such an exclusion is not required by federal law.