1.
Firstly, they're getting some
exercise, which is
always good for you.
2. It's great for your health and helps you to relax.
3. At the same time, they're having fun together...
4. ... which is important because it builds up their social relationships and their friendships.
5. Also, it's good to see girls playing serious sports.
6. I think it goes against the idea that boys have better athletic ability than girls.