Have kids when you are young.
I had the two oldest grandsons for the day on Saturday. They are 5 years and 20 months. I was wiped out for the entire next day. I went to bad at 9pm on Saturday night and didn't get up until 8:30am Sunday morning. Granted, we did do a lot and I had only got 6 hours of sleep the night before I picked them up. But, there is a reason why our bodies are biologically set to bear children when we are young - because you need all the energy you can muster! You need to be in peak physical condition to keep up with the little demons. I don't know how my daughter does it. She is a stay at home mom with three sons ages 5 years, 20 months and 4 months. The oldest is an intelligent little imp, he is never still and he never shuts up. Just him alone is enought to wear the patience of Job. I love them dearly but I am always happy to return them to their parents. Did I mention that they are little demons?