The candidates have mixed policies on accepting the donations from people too young to vote, although the newspaper said Sen. Barack Obama, D-Ill., has a policy of returning minors' money.
Monday, Obama's campaign returned $9,200 received from the 7- and 8-year-old son and daughter of Maryland real estate developer Aris Mardirossian. He told the newspaper the money came from the children's trust funds.
"It is their money and the trustee makes the decisions on their behalf," he said.
By law, individual contributions are capped at $2,300 each for primary and general elections.
The Center for Responsive Politics said primary candidates have received 1,079 donations from students worth about $2 million.
Center spokesman Paul Ryan told USA Today donations from children are suspect.
"Chances are slim that a 6- or 7-year-old would knowingly give their money to a candidate," Ryan said. "They would prefer to spend their money on G.I. Joes or Barbie dolls."