Should an U7 coach ever mention the score between games?

It is fine to talk about what happened in the game. I would just be careful that the score is not the only evidence you use. “We conceded because we all chased the ball” can be useful if that is genuinely the picture you want them to notice. But you could also say, “When all three of us went to the ball, what space was left behind?” Now the learning is the football problem rather than the number of goals. Likewise, winning 5-0 does not automatically mean the decisions were good. At U7 I would keep the conversation short and specific. One picture, one question, then another game. The score can be part of the story. It does not need to be the headline.