13 year old with rough childhood hanging with my 7 year old son

Hello!

Our 7 year old son started to hang with a 13 year old at the park since the teenager is almost always hanging at the park, and I mean, always! We had doubt that he had it pretty rough since he really seemed to be there every time we went. He's very nice with our son, so we didn't think much of it, until we invited him to our place last weekend. We learned that he indeed has it pretty rough, he told us that his parents are constantly fighting, so he doesn't stay home. We crossed his dad on the way back home, and he didn't even recognize his son at first. He also told us that he went to a couple of foster home when he was younger because his mom couldn't take care of him.

We were happy to let him come at our place, make him dinner and play games with our son, but we're having a couple of dilemmas, hence why I'm here.

One of the problems: he really stinks... We had to clean the chairs where he sat and burn some incense stick to get rid of the stench. I don't want to make him feel bad about that, should I offer him to take a shower, wash his clothes? Have a quick talk with him to see how he takes care of his hygiene? It's not my kid, so it's not my job to take care of that, but it's stinking up my place so... Not sure what to do.

We also let our son go to the park alone with him, to give our son a bit of independence (we live in Montreal, so we're a bit more worried to let him go to the park alone with all the traffic and people), but when we went to check on them, they were hanging with homeless people (one of them was passed out), searching for empty cans to sell so they can buy candies instead of playing. I worked for a long time with the homeless and I'm not judgy, nor scared, but it still felt a bit weird. Part of me thinks that it's good for my son's resourcefulness and social skills, but another part doesn't want him to start learning bad habits.

He also came pretty early at our place the next day, around 7:30 and clearly didn't want to leave anytime soon, we had to tell him to leave at 16:30 since we had some friends coming over and needed to get rid of the stench. We're happy to see our son having someone to play with, but we also felt a bit "invaded" if that's the right word.

I need to reiterate that the 13 years old is really sweet. He even took the initiative to prepare a cute romantic table with our son for me and my wife with candles, random decorations they found in our house and nachos (literally the first time anyone prepared anything just for me and my wife!). We really want what's best for him, but we also find it a bit worrying. Neither me or my wife were interested in younger kids when we were teenagers, so we're not too sure want to make of it with all the other worrying signs. We kinda wanted to call child protection on his parents (just for a check up), but they probably already know about them since he went to foster homes.

Any tips on how to deal with the whole situation?

Edit: I said 7 year old, but he's turning 8 in 2 weeks if this changes anything. And just to clarify, we were thinking of starting to let him go to the park alone (it's +-150 meters away) but weren't sure if he was ready. The teen offered to take him there and we joined them 20 minutes later, felt like a good way to ensure his safety, but I think we'll make sure we're always there to watch them for now.