the question would be about in which tax bracket would be you and in which tax bracket would be your son.
We really need to know your and your son's taxable income besides lottery winning - to determine and compare tax liability.
If you are single and have other taxable income - assume - $25,000
you will have in 2009 - 5,700 (standard deduction) and $365(personal exemption) - so your taxable income would be $15,650 - and you will be in 15% tax bracket (up to $33,950).
Additional income from lottery winning will be taxed
$15,300 at 15% and all above - at 25%
Similarly we would determine the tax liability of your son.
However if he will use HOH filing status - up to $45,500 of taxable income will be in 15% tax bracket.
However - in case he is eligible to claim an earned income credit for the child - additional lottery winning will make him ineligible for EIC.
In additional if you have a lottery winning - you may deduct your gambling losses - however you should itemize to claim a deduction and losses are limited by the winning amount.
So we really need additional information to estimate and compare tax liability.
Let me know if you need any help.