Hi, I'm trying to switch the mag wheels on my son's Mongoose (probably about 8 years old) to spoke wheels. The tires on his wheels now say 20 x 1.95. Since I'll probably just keep the tires, what size spoke wheel should I be looking for? And is there anything else I have to consider when looking for new wheels. Thanks.

You want wheels with a 20” (451 mm) diameter.
And you probably want to check the type of hub.
BMXes can have both freewheel and cassette hubs.
Cassette hubs use a smaller rear sprocket and may not work that well with a BMX set up for a freewheel hub.
Wheels may be sold w/o sprocket/freewheel, so you might need to buy the right tool to transfer yours.

Thanks for your help. I'm not sure what type of hub it has, it looks like 1 "gear" on the rear wheel/hub.

”Cassette” for BMX doesn’t mean the same as it does for multi-gear bikes.
BMXes traditionally used freewheels, where sprocket and the ratchet mechanism that allows for freewheeling were treated as one unit.
Nowadays there”s ALSO the ”cassette” design where the sprocket is a SEPARATE part, held on by a lockring.
You need to figure out which one you’ve got.

I love the mags tho.

Go to a bike shop,..

I'm taking on the hobby so I'd like to slowly learn how to do these things my self. I know I could go to a bike shop but thanks for the advice.

Well,...a local bike shop (LBS) will usually teach you about bikes if you ask. This way you get to see, and be hands on.

When I saw "Mongoose" and "Mags" I thought: "Someone actually still has Mongoose Motomags!?" Then I saw it is only eight years old. Thanks for the trip down memory lane. I would also add - unless you already decided - consider alloy versus steel rims.

If you are looking to stick with the tires you have, a set of standard 20x1.75 rims will probably be the most inexpensive and easiest to find.

If the rear freewheel/cassette looks super small (9T) then that's fairly modern (New School) and you will likely be able to find a parts bike on craigslist or something that will have what you are looking for. Otherwise, 16t freewheels were pretty standard in the old-mid school stuff. Often available used with minor servicing required. As others have said, look for aluminum hoops, and if possible, multi-wall for strength. Old single wall cheap steelies are often not even worth using unless its "period correct". You will likely have 36 spoke options or 48 spokes... 48s are typically for trick riding as they are a little stronger. 36s are race/standard equipment on a lot of stuff and likely more common to find used if that's your thing.

Out of curiosity, what kind of mags are on the thing? I love mags. I have Skyways, O.G.Ks, and Troxel Trakmasters on some of my bikes... I think i just like them because they require less maintenance haha.

FWIW, Skyway 'tuff wheels' use a nylon-fiberglass composite , optional; a nylon carbon composite..