I am moving into a rental property that does not have a bath, but have a 3 year old who loves his baths. Is there a product on the market that can be fitted into a shower recess, to hold water and allow children to have a splash – like a removable shower-sized bath? Or a plastic or inflatable toddler size bath (baby baths are too small)? Thanks

The shower stall is likely not water tight any higher thhan 3-4". Since this is a rental I would suggest something like a muck bucket Muck Bucket or better yet a small plastic child's swimming pool sold at places like Walmart.

Largest plastic storage bin you can find at Home Depot or Lowe's that will fit in the shower stall.

If your floors are water safe (not wood or carpet), put a washrag over the drain and fill to near the bottom of the curb of the shower. This will get you 3-4 inches of water.