I have seen people install a tension-fit shower rod across the back wall of the tub/shower and use it to hang plastic baskets for toys and shampoo, etc. Very easy, inexpensive, flexible, and temporary (the kids won't always have a tub full of toys).

You could also throw all the toys in a mesh drawstring bag and hang it from the shower wall with a hook.

My daughter has one of these stuck on the bath wall

I shake out the toys and put them in the baby's plastic tub, and store the baby tub in the alcove bathtub with the shower curtain closed. If I'm feeling lazy I wait until the morning, when the toys are totally dry.

The baby tub full of toys only comes out of the bathtub when someone is showering or bathing, when I put it just outside the bathtub, and guests don't see it unless they are using the bathtub.

Also helps my 3 year old forget about the toys when he is not supposed to be playing with them....

I sewed 2 loops of ribbon onto the corners of a cheap lingerie mesh bag. Then I hung those loops on 2 Command hooks mounted on the wall. Total cost Not the most attractive solution but I've given up on attractive when it comes to kids' toys and settle for organized. I didn't want to pay for a neon pink toy net and this accomplishes the same thing for cheap and I can throw it in the wash if it gets dingy. I've had it up for maybe 6 months and everything is holding up perfectly. When all her toys are in there, it is pretty full!