There are so many good water bottle options for kids. My non-negotiables are that they don't leak, are simple for the kid to use and are easy to clean. These are the best:
--> Snug water bottles check all these boxes. They have a soft straw, a simple lid that opens with the touch of a button and come in adorable patterns. They are narrow enough for a cup holder and come in a 12 or 17 oz option.
Linked here.
-->Takeya is the best for a hard, foldable straw water bottle. Convenient loop handle for kids to hang on to and keeps your water cold for 24 hours. 14 oz and comes in several great colorways. Hydroflask is another great brand, very similar functionality, just slightly more expensive.
Linked here.