How do I get my husband legalized if he entered the U.S. illegally, twelve years ago?

You cannot get legal status for your husband, unless the Congress changes the law. Meanwhile, a couple of words of advice. First, tell your husband to stay away from all trouble: Immigration will not look for him, but if he gets arrested he will end up in Immigration custody and in removal proceedings. You would not believe how many people get deported for drunk driving, for trying to ride a bus without payment, or for being caught in the middle of a bar brawl. Second, take him off your public assistance case: he is not eligible for these programs, and receiving them is fraud. Sooner or later, he will have to answer for it. I know that taking your husband off public support can make your life even more difficult when it already is, but keeping him on these programs will likely disqualify him from getting a green card. Third, your husband should - if he can - maintain relationship with his son, the closer the better. The more both his children need him, the more reasons Immigration Court will have not to deport your husband. Fourth, find an immigration attorney who will know your husband's case and will be ready to step in when Immigration arrests your husband.

A more detailed information is necessary before a determination can be made with respect to how you can fix your husband's immigration case. However, some issues can be clarified without having those information. First, a necessary first step is that you need to file a Form I-130 petition for your husband. But, he may not be eligible to receive a green card if he entered the US without inspection and must instead return to his country for consular processing. His several years of unlawful presence is grounds for denial of his visa once he returns to his country and must be eligible in addition for a waiver based on showing of hardship to you and your US children. Despite all of these, I strongly caution that even before filing anything with CIS, you need to consult with an experienced immigration lawyer. If your husband has previous violations of immigration law including previous order of removal or if he was ever convicted of crimes, filing anything with DHS at this time will bring ICE to your door.

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. Since you are receiving government benefits, you may not qualify financially for the Affidavit of Support and will need a co-sponsor for your husband. Your husband may also need a waiver for his illegal entry and overstay and may have to go back to his country for consular processing.

It's like doing a very complex tax return. I'd strongly recommend you hire a board certified immigration lawyer like myself. The starting point is the visa petition process, but that's just step one.