
By the time a child tells you they’re thirsty, they probably should have had a drink a while ago.
Offer drinks at the natural points of the day, like before you leave, when you arrive to your destination, and when getting back home.
With kids, it helps to connect drinking to something that is already happening. Everyone takes a sip when you reapply sunscreen. Everyone drinks before leaving the playground.
Plain water is the obvious everyday choice, and some children will happily drink it. Plenty of others will carry the same full bottle around all afternoon.
A little flavor can make a big bottle much easier to finish.
Try adding:

This applies to adults too. Some people, particularly in pregnancy, may find that plain water sends them straight to the bathroom without leaving them feeling particularly hydrated. Flavored water such as Neviot or Schweppes, or a little juice added to a bottle, can feel much easier to drink throughout the day.
Some of the best hydration on a hot day comes on a plate.
Water-rich foods do not replace drinks, but they help, especially with children who seem to view their water bottle as decoration.
Good options include:
Warm water that has been sitting at the bottom of the stroller for three hours is not appealing to anyone.
A few simple habits help:

Give each child their own bottle, preferably one they easily recognize. It makes it much easier to see who has been drinking and who has been carrying around a full bottle all day.
Keep bottles somewhere children can see and reach them too.
The best hydration plan is the one your family will be able to keep up with.