Gifts up to $14,000 in 2013 are not taxable for gift tax purposes (they are never taxable for income tax purposes, regardless of amount). The additional $1,000 per child could be taxable, although your mom can apply part of her lifetime exemption ($5.25 million in 2013) to offset this additional gift with no current gift tax. However, if you and your siblings are obligated to use the funds for your mom’s benefit, then there is no gift and no tax consequences.
An amount taken from income as a prepayment of an individual’s tax liability for the year. In the case of wages, the employer withholds part of every wage payment. Backup withholding from dividend or interest income is required if you do not provide the payer with a correct taxpayer identification number. Withholding on pensions and IRAs is automatic unless you elect to waive withholding.