This page explains what a contrast extravasation is, how it is treated, and symptoms to watch for. DOWNLOADABLE PDF: Contrast Extravasation.
The amount of fluid a child needs depends on many factors including their age, their gender, the weather and how much physical activity they do, but generally they should aim to drink about 6-8 glasses of fluid per day (on top of the water provided by food in their diet).
They suggest that infants over six months may have limits amounts of juice each day, reserving the limit of 4-6 ounces for children between the ages of 1 to 6 years. Keep in mind that this is really a daily limit though and not necessarily an endorsement for drinking juice.