Children don't wanna "eat their vegetables" for two reasons, first and mainly, they're mostly given cooked vegetables, which have plenty of toxic compounds and offer very little if any health benefits, and for many kids are particularly harmful as they're unable to utilize the mutilated nutrients without them causing lots of damage, because they lack the proper enzymes for breaking down the mutated cooked nutrients. I had access to plenty of raw vegetables as a kid and loved all of them. The produce guy used to call me celery kid when I was 2-3 years old because when I went shopping with my mother, and she bought celery, I'd grab a piece immediately and start eating it right there. She always tried to take it away from me so we could get home and wash it first, she was probably concerned with bacteria mostly, although there were probably pesticides too, but apparently I didn't care.
The second reason is that children being so young and small, don't have as many toxins to remove from their bodies, so they have less of a need for the detoxifying power of vegetables. Also, even if they do have plenty of toxins, their bodies just don't have the necessary nutrients to safely detoxify in large amounts, especially while spending so many nutrients in growing at the same time.
