I think sometimes, the more of an issue you make it, the more the kids dig their heels in. Just like food, I'd offer her water/milk as usual. She gets to decide to drink or not. A four year old is old enough to figure out if she's thirsty or not. She'll drink when she's ready...even if it means she waits until she gets home and drinks juice. Food/water are part of a battle I refuse to engage in with kids because I know I won't win. If it's that hot or she's that active that heat exhaustion is a real concern, I'd give her a choice - sit quietly in the shade or drink something but I'd leave the choice up to her.

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