Sibling rivalry is strong within our ranks and there is no cease-fire just because they are riding in the jogging stroller.
Type 1: The Fair-Fight
The petite 5-year-old and the enormous 3-year-old. Things will be going along fine until one of their little feet starts to cross over the mid-line and the next thing I know there are arms and legs flailing and the stroller is jerking around and we are quite the spectacle!
Type 2: The Bully
The 3-year-old and the newborn. Not a fair fight. What begins as innocent hand holding often escalated to arm squeezing and eye poking. Defending the baby is required.
Solutions - well, preventions, hopefully, to the fighting are mainly about distraction! Food, books, music, etc. Books are especially useful to create a physical wall between the two kids as well. Covering the baby with a blanket when the weather allows for it also provides a physical barrier.
Keep the older child's eyes "out" of the stroller looking for red cars or squirrels or whatever you are likely to see along your route. Keep the older child's hands busy with small toys, an old iPod, coloring, binoculars, songs with hand motions such as "Itsy-Bitsy Spider" or "The Wheels on the Stoller," etc.