As many as 350,000 households are not getting the $300 per child refund owed as part of economic stimulus rebate payments.

The Internal Revenue Service says taxpayers' error and problems with commercial tax preparation software were responsible for the problem affecting a tiny percentage of the 130 million taxpayers expected to benefit from the refunds the government began sending out last month.

IRS spokesman Terry Lemons said the agency is confident it has identified all the people affected by the mistake. He said the IRS will send letters to those who missed out on the refund and that checks for the child credit will be mailed in July.

Lemons said people do not need to contact the IRS or file additional paperwork.