I won't give my nephew koolaid, or most fruit drinks because legally they can carry as little as 5% juice.
Normally he mostly gets water. I tell him, we're like 78% water and we need to drink lots of it to be healthy. When he does have juice it's from consintrate and I add extra water.
Soda is forbidden, which lands me in trouble because what do you think Grandma gives him? Root beer or worse Pepsi...not only enough surgar to make him buzzed for a week but caffiene!
With his Dad, he lives on Mac & cheese and frozen pizza. After a few days he comes to me feeling, tired, whiny, and it's like well when did you last have a glass of water? When did you last have a good meal?
Feed him a good dinner, with most of the food groups and a couple glasses of water and he feels much better, he listens and he doesn't whine! Sure some days we'll have pizza, or fish sticks but if we have one junk food meal, the other is good things like meat, potatos, other veggies.
I slice an apple and sprnkle a little bit of cinnimon and sugar on it. My nephew loves it.
Dip. Seriously, if you can't get a kid to eat veggies, give them salad dressing to dip it in and TA DA.