You are right, I went to a nutritionist a few years ago and she told me that a full bagel is about 3 servings of grain and I used to think that was 1 serving. I always thought I was way under on my daily grain servings but it turned out it was over and bread items are not my favourite part of the meal. I seem to remember her telling me that the Canada Food Guide had reduced the sizes of the servings several years back.
I think the rule of thumb to feed the children is to give a good balance of diary/protein/grains/fruits/veggies throughout the day and to make sure you have full tummies all around without letting them go crazy and limit the sugar. If you do that you are doing a good job.