Should U7s be encouraged to celebrate goals together?

I’d leave most of it to them. Celebrating together can be a lovely sign that they feel part of a team, but I would not turn it into something they have to perform after every goal. Some children want a high five, some want to sprint back, and some are already thinking about the next restart. I might encourage simple things like recognising a teammate who helped create the goal, but even that can be very light-touch. The useful social learning is probably bigger than the celebration itself: can they enjoy scoring without mocking the other team, can they be happy for a teammate, and can they settle ready for the next game? If their natural celebration is joyful and respectful, I would mostly stay out of it.