Either Rust-Oleum or Krylon make excellent spray paints. Clean first with TSP, letting dry over night. If you don't have a place where you can safely spray paint them you might want to check with a local owner operated auto paint shop and see how much it would cost to have them painted for you.

Krylon does make a water based spray paint. I've used it and it's excellent. Very smooth. KrylonH20

Rust-Oleum also makes one too, but I've not yet used it. RustOeum Aqua

Can I use wall paint I already have? Or do I have to specifically use metal paint? I want it to match the colors I've used for the room...and I have more than enough left...hoping to make use of what I have, if I can!

I've just not had good luck with spray paint....not getting an even coat, dripping, etc etc...I'd prefer to brush it on, whatever I use!

Thanks for the input so far!

(these will be in a bedroom...I don't need to worry about the elements)

I would not recommend using latex, most likely it will peel. Maybe if you sanded and primed with an oil primer first, but then I would say you'd have to apply a protective finish on top of the latex.

Plaid makes a no-prep metal paint (water-based) that comes in 2oz tubes. Michael's carries it (not sure what other craft stores), otherwise it's available on-line. Clean the surface and paint. You can mix your own color or use straight from the tube. I found it by accident a few years ago and I swear by it. I know of others on this forum who have used it with much success.
Although, a large surface may be a little tricky and you may need to do a few coats to get it even. Spraying with a no-prep metal paint is the easiest.
If you're set on using the latex, test it out on the back and see how badly it scratches/peels.

Sanding would be ideal, but they're making nice improvements with bonding primers. You might try Ace Royal Sealing Primer, Ben Moore Fresh Start Superior Primer, Zinsser Bullseye 123 or Cover Stain, Sherwin Williams Adhesion, or Glidden Gripper (I believe all of the above say they'll adhere to glossy surfaces and oil or latex, but always double check the label before using a product). Paintergirl is right about the peeling of latex on heavily used items, though. I painted my bathroom vanity 7 months ago, and what started as a tiny chip on a shelf is trying to peel away into a bigger spot (I'll be going sanding & over it again with Ace Cabinet & Trim Paint, which is hard like oil but cleans up easily like latex). If your son is going to use that locker as hard as we did the ones in school, I'd definitely consider a protective top coat like poly (regardless of whether you use latex or spraypaint). Oh, and latex paint takes up to a month to fully cure, so if you go that route, you'll want to let it cure for a while (ideally a month, but a week would help) before putting it into service. HTH!

Yes you could use your latex paint, but it's not going to look as professional as it would sprayed. Do you have a paint sprayer or know of someone that does that would let you use it?
If not you might try a foam roller for a smoother finish.

Sanding does not involve removing the current layer of paint. You just need to lightly sand to give the next layer of paint something to grab onto. You should be able to sand each one of them in less than 10 minutes.

Thanks for all of the input! Hubby actually bought this little paint sprayer when we painted our chicken coop inside...worked well.....if I can remember how to put it all back together! I was afraid it might peel...I'll look into others.

Thanks, graywings...don't know why I've been dreading the sanding so much...your post makes it sound like it'll be a breeze if I did. The plan is to try with one locker now (we have two) and see how it goes. One is white....it can stay white if need be, but the blue one has got to go!

Get a brown scotch brite pad and scuff the existing paint. You just really need to remove the shine. After that wipe it down really well with a tack cloth and then paint away.

I do this all the time with metal products.

Please come back and share pictures and any info that might help others wanting to paint something similar. Glad you have a sprayer though. I'm thinking it'll look just fine.