Black Out Blind for Child's Naps

I would put him in the darkest room to nap.
Or throw a blanket over the rod.
(But honestly, I've never had this be an issue in any house/condo we've ever rented.)

black trash bags and scotch tape. :)
portable, cheap, easy.

well, it wouldn't come up for us because our kids napped where they napped. no need for blackout blinds or white noise machines or any of the other sleep crutches so popular now.
and in a rental, why not just hang up a blanket or beach towel or something? why buy a blind for a vacation rental?
khairete
S.

I've just draped a large inexpensive blanket over the rod..... helps block out heat and light.

Let the sun in. Enjoy it. Good for the mind and body!

llarge towels and safety pins to stick it to the existing curtain

Walmart sells really good blackout panel curtains. Perhaps use some clips to attach them to the top?

ETA: Oooh! Or put them in the bathroom! (Kidding, kidding)

Since you are staying in a rental I will suggest asking the landlord if you can hang something or if they can have it done.

I own and manage a short term rental here in Florida and I would be very upset if someone added holes to my walls for an extra curtain, I would also keep the deposit. I put vertical blinds on my sliding doors (and windows) that are room darkening, I would think if these doors are in a bedroom they would have done the same.

Push pins and large beach towels make great temporary black out blinds.
When we moved into our new house, this system worked temporarily until we got more permanent solutions.
If a towel is too heavy then try hanging up a large plastic beach mat - that should be more light weight and it should block the light fairly well.

I'd just bring a blanket and hang it over the curtain rod. Although most likely your son will be plenty tired and a little light won't hurt. Being able to nap in less-than-ideal circumstances is a precious gift. I would encourage it at every chance.

I believe Bed Bath and Beyond has a liner you can clip or pin to existing curtains. Called "Sound Asleep".

Put some newspapers over the window and use painters tape to adhere them. You can leave them up the whole time or take them down each day.

How about a black out roller shade from Home Depot. Instead of mounting it you could just rest it on the existing curtain rod and pull the shade down.

We use that - I bought a piece of fake leather (like naugahyde) at a fabric store, in the remnant section where they have upholstery fabrics. It was pretty much light-proof. You might also consider tablecloth fabric, the type that is waterproof and therefore has an extra layer or coating on it, beyond what typical material has. You can also buy black-out lining fabric that is designed to be added as an extra layer to any fabric - it comes in a roll and is sometimes packaged in plastic vs. being on a display roll as decorative fabrics are. If you ask someone knowledgeable in a sewing store, you'll get good help.

I attached some curtain hooks to it, the kind with the sharp pin on one end that went through the fabric, and a hook on the other end that went over the existing curtain rod. We also took a few clothespins and other handy hardware to rig up our own system depending on what we found at the rental. Things to consider are small nails (nail into the top of the window frame where it's not visible), picture wire or strong twine, a small hammer, duct tape and a yardstick or other long, thing item you can affix to a curtain-less window and hang the black out fabric from.