Robb, I love my nieces dearly, but I also think they broke my biological clock, if I ever had one.
I have the perfect arrangement. I play with them for a few hours and when they get cranky, I leave. :)
Finish each day and be done with it. You have done what you could. Some blunders and absurdities no doubt crept in; forget them as soon as you can. Tomorrow is a new day; begin it well and serenely and with too high a spirit to be enbered with your old nonsense. ~ Emerson