No one can "just go down to family court one afternoon and steal a child." And even if she could, she couldn't do it without your knowledge. You would have been served with a copy of her petition or complaint and given instructions what to do about it. Nor can she legally deny you access to your place of residence without a proper eviction, even if she is your mother and she owns the house. She's blowing smoke and she will get away with it as long as you let her. The police cannot help you. They only enforce the law. They can't interpret the law or give legal advice. Without a court order to enforce they are powerless.
It seems you're living under your mother's thumb, possibly because of your perception of financial dependence. If you want your son you're going to have to grow a spine, call her bluff and get your son -- and you -- out of there ASAP. You can start by demanding to see this so-called guardianship order and restraining order. I'll lay odds she can't produce either one, but if she does, read them carefully. If they're not signed by a judge and file-stamped by the court clerk, they're not worth the paper they're printed on.
If you need encouragement, a local family law attorney can explain in detail your rights and possible options under your particular circumstances and your unidentified state's laws.