I’m big into motorcycles. I love motorcycles. I commute, run many of my errands, go on vacations, and race.
Using a motorcycle with a sidecar to transport your kids will in no way be more efficient than a small car. A motorcycle big enough to move a sidecar that will carry two kids will get way less than 50mpg. Additionally they’ve got all the disadvantages of both a motorcycle and a car. They’re big, unprotected, and difficult to handle. And a good one is not cheap. You’d be better off with a Civic.
Can’t argue with the cool factor though.