Nalgene On-The-Fly Kids Bottle w/Graphic, 12 oz, Green with Sprout Cap, 12oz, 1263-0027

It features everything thats made its grown-up version wildly popular (one-handed opening leak-proof design durability odor resistance) but its 12-ounce size is more manageable for little hands and thirsts. Its carabineer friendly too so hook it to their backpack or your daypack and get out there.