My neighbor is a thief

I think my 12 year-old neighbor kid is stealing my son's stuff. Every time he is over, something comes up missing in the next day or two. For example, this past Sunday he needed to come over to use our internet for some practice tests for school. My husband had taken the boys fishing so the only people in the house were me, the boy and Olivia. I had been on the front porch while Olivia was napping talking to my sister on the phone for about 30 minutes. When I came back in I saw him coming down the steps. I was immediately suspicious because there was absolutely no reason for him to be upstairs and he has taken things from Sam before. He said he was using the bathroom. I told him there's a bathroom downstairs. As a matter of fact, you have to walk right past the bathroom to even get to the stairs. He then laughed nervously and said,"Oh yeah, I keep forgetting that!" We all live in military housing, so for those of you who don't know....every single house is exactly the same. He didn't forget. So I casually walk myself up the stairs and start looking around Sam's room to see if I notice anything missing. The first thing that caught my eye were his Tech Decks. They're these little skateboard things that he likes to collect. There were three sitting on top of his bookshelf, but I couldn't remember if there were supposed to be four or not. I just could not really tell so I left it alone....until this morning.

Now, it's been a crazy week and the weather has been all yucky so there has not been a single kid upstairs since Sunday. The last kid in the house that went upstairs was the neighbor boy. Sam called down to me this morning asking where his fourth Tech Deck was. I immediately stopped and I knew instantly where it was. I told Sam I wasn't sure and promised to help him look later, but quickly shooed him off to the bus. Now that he's gone I'm steaming mad. I don't even know what to do about it! I can't just all of the sudden forbid the boy from my house. I can't run over telling his mom that she's got a klepto on her hands - I have no proof!! If I were in that position, I would want proof. What mom is gonna look at her own kid's sweet face and not believe him when he says, "I swear, MOM, I didn't take anything!!" This boy is not a little one anymore - he's 12 - he needs something to fill a void that has surfaced. Their family is new to the Army and their father is looking at his first deployment in a month or two. The boy's grades have been suffering and he's been fighting with his parents. Now I have to figure out a way to tell them that I think he's been taking Sam's stuff too! Oh my God what do I do? I'm so mad I can hardly see straight. What's worse is that I've given them all the advice I can without sounding obnoxious and they just look at me like I'm crazy! She tells me he's not finishing his homework, I tell her to have him sit down and do it as soon as he gets home from school. Pretty obvious, I think, but she looked at me and said, "He's 12, I should not have to sit down and make him do his work." The way she said it told me that she was not receptive to my idea so I just dropped it.

They've got a lot of issues over there and I don't want to make it worse. The things that have gone missing are not that expensive, but it's the principle of the matter and I, honestly, do NOT want him in my house anymore. What do I do?