You will owe 15% SE tax on your net profit from the 1099 (gross income minus expenses, if you have any) so about $1650. Then if you file jointly with your spouse and assuming you are middle class, you are in the 15% or 25% tax bracket and will owe another $1650 to $2750 in income tax. You will have a schedule C that computes the net profit from your self employment and that income will flow to the rest of your tax return with any other income (W-2 jobs, investments, etc.)
If you file jointly, your self employment income will be added to your spouse's income and all your personal deductions, dependents and credits will be considered together as one tax return. The total tax is calculated and, with $11K of self-employment, you will owe about $4000 more than usual, or your refund will be $4000 less than usual. If continuing to do this work, you will want to set aside a portion of your self employment pay to cover estimated taxes.
If you filed married filing separately, and claimed one or both children as dependents, you could owe no income tax, but still owe the $1650 of SE tax. However, that would mean that your husband would also have to file separately, and would have no children to claim, which would cause him to owe a lot more.
Joint filing is almost always better because the tax rates are lower and certain deductions and credits are disallowed or reduced for married filing separately. The only way to know for sure is to test it both ways. One word of caution -- if filing separately and one spouse itemizes their personal deductions, both spouses must itemize even if there are no itemized deductions to go around. You can't stack all the itemized deductions on one spouse and have the other spouse claim the standard deduction. (This applies to personal deductions like state and local taxes, mortgage and property tax, and charitable donations. Business deductions are handled separately.)
