I attended a wonderful workshop once on creating healthy eating habits and one of the best advice I ever heard came from there

Our job as the adult is to provide access to healthy food options at regular intervals and set the 'expectations/rules' for etiquette at the table ~ it is the child's job to decide IF and HOW MUCH they will eat within those regular intervals and rules ... aka if the rule is you sit at the table until you are finished and the kid leaves and than tries to come back well he'd be DONE because that was the rule you set as the adult ~ aka no up and down from the table when you leave that means your done!

They suggest that this is BEST because than children can learn to self regulate their own 'hunger / feeling of fullness' ... and the more we push them to eat stuff, make a big deal and so forth the more we 'interfere' with the development of that self regulation and create picky eaters, binge eaters, children who do not know their 'full' feeling and overeat cause they were constantly encouraged to eat as babies when they were indeed 'full' .... fact is that some children are morning eaters and will consume most of their calories in the morning and than taper off and nibble in the afternoon and evening and others are opposite and will pick breakfast and snack and than eat more at lunch and evening meals.

My snacks both morning and afternoon basically consistent of unlimited fresh fruit and protein but only one grain serving
Lunch is unlimited protein, veggies and fresh fruit and one grain serving
Water is served with all snacks and meals to encourage them to 'eat' their calories and not drink them ~ their 'dairy' serving is covered in their meal.

I serve 'small portions' of each food group to start to reduce waste and will offer seconds, thirds and so forth until either what I prepared is 'gone' or they are saying they are 'full' ... if there are leftovers that have not been touched than they get packaged up for my spouse to take next day for his lunch if they have eaten everything I had prepared and are still hungry I will serve more fruit or veggie.