Best protectant would be paint over primer.

Second best would be an opaque deck stain.
Clear stains do not last under the suns UV bombardment like the denser opaque varieties.

Any finish will 'rub' off, painting the support pieces and staining the seats/ladders/areas that will get wear would be the longest lasting solution for your requirements. (Since the stain would 'rub/flake' less than the paint under use.)

While I agree with Handymac, here is the one I used on my granddaughter's set. I got it at the corner hardware store (Do It Best franchise)

Consumer Reports regularly reviews various deck sealant products. I've not seen one recently, but a while ago, Thompson's Water Seal was about the closest thing to no
finish there was. It barely made it through a season.

Here is a link that might be useful: One Time

Thanks so much for the info about One Time. That sounds like the way to go assuming I can use it in my case. The set is 10+ years old. I'm assuming the previous owners used an acrylic latex stain and I can't use the One Time cleaner to get it off (according to their website). I have powerwashed and sanded the set and gotten the majority off. I have written One Time to see if I can still use their product effectively with what I have done so far to prep the wood.

Did you just recently use One Time on your granddaughter's set or has it been on for a year or more? Would like to know what your review is of the product thus far.

Thanks a ton!!
Jody

It's been on two full summers. I was just on it today to pull off the swings for the winter and it looks good yet.

bobsmyuncle - What did you do to prepare the set? Did you use stain stripper, powerwashing, or what? As I mentioned, we have powerwashed and sanded, but there is still some of the old stain in places. Since the One Time is so expensive, I don't want to waste it by not prepping the wood right. Do you think I should go buy some stain stripper to be safe and apply it to the whole set?