How can our child take part in events (sports days, recitals) without it being too much?

Instead of "all or nothing," think in terms of partial participation and participation through a role. They can join only the events they're able to, stand at the end of the row for the opening ceremony, or help with setup if the main event is too hard. Familiar approaches include: giving them a sense of what to expect ahead of time with photos or videos of the venue, deciding on a cool-down spot and a signal to step away on the day, and talking things over with the teacher starting from the practice stage. Even if it means adjusting the form of participation, aim to end on a success.