Yes you can drink freely during meals and the kids can help themselves to juice or fizzy drinks.
The buffet at kids paradise is limited to chips, chicken, spaghetti, salad, etc. nowhere near as nice as the main restaurants but we did use it several times last year as we had 4 children with us and just wanted a quick snack, mainly for them. You can also get ice-creams here so we'd get one and take it back to our sunbeds. You'll have a fab time, there's loads for the kids, how old are they? Mine were 10, 7 and twins 5 last year and they had a brilliant time at the clubs and doing all the activities. Make sure they take part in the rehearsals for the once a week kids show, they are tremendous and the costumes fabulous. The children may enjoy taking dinner on their own in the kids section of the main restaurant, ours certainly did. This allowed them to go back to the clubs whilst we ate a leisurely meal alone, a real treat on the odd night!
As others have said there are regular dolmus' that take you back to the residence so there's no real need to walk, though i reckon it'll take you about 15 mins at most.