Money missing.

So the other day I had 100$ bill in my wallet with 2 $1’s behind it. My purse was sitting on my couch. My husband was asleep all day and all night didn’t bat an eyelid. The 100$ the next morning is GONE. Everyone knew that it wasn’t my money and had to be returned to the person when they got back in town. Then on Friday I got my check well some of it and I had to give my mom 300$ so I counted it as I handed it to her. She takes it puts it in her bra and it’s done. My debt is paid. Well I told her I would take her money and card and put it in her purse because I was going downstairs. So I do exactly that. I told her I flipped her jacket over her purse so that way it wasn’t like look at me. The only ones that go in my basement is her, and my 9 year old step son and 8 year old daughter. So yesterday my daughter has a dance competition my mom hands me 40$ for us to get in. I only use 14. We get home I am laying my 2 year old down and my mom texts me and says 194$ is missing from my wallet. WTF are you kidding me. My husband wasn’t home so it couldn’t have been him. It wasn’t me cause it was my debt owed. And my 8 year old daughter is so nieve she wouldn’t think to do that. I hate to point fingers here but I have a strong gut feeling my step son is stealing our money. He has been sneaking my husbands cigarettes, he is always being sneaky. But 300$ in a week we have had him back is a lot of money. What do I do? I am getting ready to flip his room upside down. I have checked his back pack his pockets. Things like that. But I haven’t said anything to him. I am so beyond beyond myself that I can’t wrap my head around it.