Our favorite toy has been an Indian-style lota. My kid loves having the narrow spout to pour over bubbles, fill cups, etc., and it’s great from my perspective for washing hair or other body parts (we don’t have a removable shower head.

Ours is made from HDPE, which I consider to be the safest of the plastics. I feel like it’s really unlikely to leach anything at bath temperature.

I can’t find the exact one we have, but this is similar: https://www.amazon.com/Mayaka786-Blue-Lota-Bodna-Toilet/dp/B00UBHTPNU