A mom just conveyed this common dilemma to me:
You go out with your bike trailer and get a great workout hauling your little kid around, especially up the hills. Then, you get home and want to relax and your passenger is full of energy. What's the solution?
Let your child(ren) out to run around or bike around on their own after your ride. I even announce that this is the plan ahead of time so my kids have something to look forward to. A one year old will be happy just running around the yard. A two year old might be able to pedal around on a tricycle or trike, and a three year old could be on training wheels or on a no-pedal bike. The idea is to let kids get exercise just like you. You might need 45 minutes and they might need five or twenty-five, depending on the age and ability of the child, and on the day.