I've washed them up, or mix them in with different foods. Right now my kiddo love just about anything covered in a red curry sauce. And other times all he eats is gold fish.
Try mixing it with meat. Let's say dumpling, make it a mixture of dumpling and a little portion of meat. Do it again without the meat. Don't reveal to them immediately. Do it little by little.
If your kids like apple and orange juice try this one-
4 whole apples
2 whole carrots
2 oranges
Juice them up and then it'll come out as orange juice. Then gradually increase the amount of veggie/fruit ratio.
Even let your kids pick 2 fresh fruits from the grocery store and one veggie you want them to try ( parents choose this if your kid does not want veggies)
make it a fun activity of making juice and then explain where it all comes from once they are comfortable on veggies and fruit.
I highly recommend watching "Fat, sick and nearly dead" on Netflix, its about benefits of juicing proven.