You're not the only one who will have to get used to this setup. Your child will also have some things to get used to. The following are some tips from Jennifer and Michael Wardian that they use when taking their boys, Pierce and Grant, on long runs.
1) Bring along snacks. Things like crackers, gummies or bananas, things that are easy to give them and you aren't worried about them choking on.
2) Bring water. Three sippy cups work well (for a double stroller, just two for a single), one for each kid and an extra, in case someone runs out.
3) Bring toys. A couple toys for each kid works well, plus a couple extras so that, in case they want what the other has, you can regulate.
4) Have a specific goal and relay that to the kids so that they know. You can tell them that you're doing an out-and-back or a loop, or describe the turn-around point to look for. Have some idea of where you are in the run so you can tell them how much longer (because they will ask).
5) If they want to stop along the way, tell them we can do that on the way back and then work it into the run. It is nice to stop and let them play, too. While they play, you can do jumping jacks or push-ups or just play with them; it's a great way to work on general strength and balancing muscles.