Hey Good Deal it's nice that you all was able to step up or are going to be stepping up with the purchase of a Smartphone! but with any Smartphone.. no matter the style) Android, iPhone or BlackBerry Verizon requires the Line or Lines to have some kind of Data Plan attached with them..
Now as you mentioned you wouldn't use that much there are choices you can choose from they start with the 2GB's up to 10GB's plans or you can choose the Data shared Plan this plan allows many device choices.. Phones, Tablets, and other devices that Verizon offers..
One thing to keep in mind if your kids love to Text I would Choose a Plan that has Unlimited Talk & Text then choose a Data plan that best suits your needs you can make adjustments on the Data plans just be aware that any adjustments) Verizon will pro-rate the adjustment for month you make the change) I like to make adjustments after my bill has fully Cycled as in doing that the changes are not as scary as when you do another time in the month..
Hope this helps in your Choices.. Enjoy the Phones b33