Cherish every moment, they grow up in the blink of an eye blah blah yeah whatever.
For me it's not having to go swimming with them. I hate it so much. I don't like swimming anyway and then add clambering on me, splashing me in the face and then getting changed after, wet hair, wet clothes. On holiday I took them every day. We're staying in a hotel right now and there's a pool so it's bloody swimming again. DD is 8 and can swim alone. DS is 6 so another couple of years until I can just watch from the sidelines. I can't fucking wait.