It is a constant struggle around my house to get consistent veggie flow into my kids. I always offer, but there are times when they go untouched on the dinner plate. I feel a little better about their consumption by making them a smoothie in the morning, and throwing lots of veggies in them. It is amazing what blueberries and a banana will cover!
There is no exact recipe or ratio, it is just kind of a play-with-it kind of situation. Here is my kid's favorite.
And yes, this does have a good bit of (natural) sugars, but I do not limit my kid's fruit consumption. Kid's growing bodies need different ratios of sugars and nutrients for brain development/muscle/skeletal change. The key for me is keeping the processed unhealthy sugars out, but if you want to limit even further you could cut out the banana and sub another liquid for the apple juice. Additionally, it is a trade off... I get a ton of veggies in, which for me outweighs the sugars. And as long as they are not eating them close to bedtime, it doesn't effect their sleep.
Coconut milk Kefir (or just plain coconut milk, but I like sneaking in the good bacteria)
Spinach (I use frozen/cooked broccoli as well)
A little bit of 100% apple juice, just to get the blender going (or you could use water too)