The whole year we drink mostly water, with some juice on Shabbos and an occasional can of soda that daddy brings home. Some kids drink milk in the morning, but for some reason, as we approach Pesach, in addition to "what are we going to eat?" we also have "what are we going to drink?" Those KFP Coke display beckon in every grocery store, showcasing phosphoric acid and sugar (hey, at least it is sugar and not corn syrup). One year I got a few bottles of this Coke. One of them still hung around in the summertime. When we opened it, it was completely flat and undrinkable. Lesson learned: we just do not need to spend money on these.
So, what are we going to drink?
First of all, there is water, good ole plain water. Throw a few ice cubes in it, put a dollar-store pitcher on the table, let kids go at it with permanent marker and you've got a drink. At least it is not blood.
Then, there is seltzer. Plain unflavored seltzer is kosher without needing additional Pesach supervision. Your local grocery probably has it for less that soda, and it is healthier for you.
Those two can be your base. Now you can get all fancy: float a lemon in your water. Or mint. Or cucumber, Add some frozen berries to seltzer right before serving. Make your own lemonade: squeeze some lemon juice (can be done on yom tov) or pour ReaLemon juice (also does not need special hechsher), add sugar, stir, add water, taste and adjust. Make iced tea: make two cups of strong tea, add sugar, then add water and ice to taste.
Your kids want juice? Did you know that Kirkland brand apple juice has OU-P? That makes it cheap and readily available. Tropicana also has a special Pesach run of orange juice, the containers are marked, but if you live in a jewish area, they tend to go quickly.
There are frozen juices that you reconstitute with water that are also kosher le'pesach, but I never buy them, so I cannot vouch if they are worthwhile.
Of course, you can make your own juice and drink that.
Raise your glass!