One of my daughters kept chewing on the sippy cup nipples. These are apparently chew proof. They are super simple to clean. No crevices or locking parts. They are a little tight and tough to slip on when you first get them but don’t give up!! They are totally worth the learning curve. Maybe practice with a cup of water a few times before you move up to juice or milk. :) No complaints!! Love this product.

Acorn Baby Silicone Sippy Cup Lids That Fit Any Cup 2 Pack