Why do we struggle so to say NO? We don't want our kids to be mad at us. We don't want to disappoint them. We don't want to sit in the blistering storm of their rage.
Getting a younger child to settle down in the evening, go to bed, (stay there!) and then actually fall asleep is a big challenge for many parents, and one they struggle with nightly.
Every family has their own value system and comfort level with sugar. Figure out your comfort level and consider whether you need to be a bit more flexible, or perhaps more limit setting.