Thanks to [the children] the long hours of austerity were relieved by light hearted interludes, little girls skipping while the big ones danced.
Like the second side of a coin, where the last chapter spoke of the isolation imposed on the children, here we learn that their joy and happiness had an impact on the sisters. Children will be children, and even if these were living in a strict and somewhat limiting environment, it was still one that gave them room to grow, and blossom and bloom. Here we see that they still ran, and laughed, and played. Not only that, we see that it brought an element of joy and happiness to the convent itself.
It will be interesting to see what else we learn about this tension here. I guess we keep reading!