If you are married, you have the option of filing jointly or separately. If you file as married filing separately, you can claim all the children, and you don't need to file as an injured spouse, because you are filing a separate return. However, some tax credits and deductions are reduced or disallowed and the rates are higher.
If you file separately and you itemize your deductions on schedule A, your spouse is not entitled to any standard deduction and must file a tax return if his income is more than $5.
When you are married, you are always allowed to file jointly. You must report ALL your income of both spouses, even if some items are small. You will benefit from lower tax rates and better deductions, but you will have to include the injured spouse form in your situation.
One final point that may be worth discussing. When you file a joint return, you are taking joint liability for all the income, deductions, and other claims on the tax return. If it later turns out that one spouse was cheating on their taxes (hiding income, working under the table, etc.) then both spouses are equally and jointly liable, and the IRS can come after either or both spouses, including the spouse with more money, even if they weren't the actual tax cheat, and even years after a possible future divorce (because you voluntarily signed a joint return taking joint and equal responsibility). Filing as married filing separately protects you from this situation because you are only responsible for yourself, although you may pay higher taxes.
