1. written agreement: children and parents can sign a written agreement stating that the money is entrusted by the children to their parents for safekeeping, including the amount, purpose and duration. This agreement is legally valid by both parties, and the backup is kept as evidence.

2. Bank transfer record: children can directly transfer money to their parents' bank accounts through bank transfer. Make sure that the transfer record shows the transfer and receipt of the money and the purpose of the money.

3. Witness testimony: The person who witnessed the transaction as a witness can provide testimony to prove that the funds were handed over by the children to their parents. Testimony can be oral testimony or written proof.