This was today. It was hot but we survived 9 innings (well, sort of) and ran the bases after the game.
Some notes:
(1) Having grandma there helped. My daughter was unsure if she wanted to see an MLB game but was sure she wanted to see grandma.
(2) Having good seats helped - my instinct was to get the cheapest possible seats because of the risk we'd go home early, but grandma convinced us to shell out for nice seats down the right field line. Being close to action helped.
(3) Speaking of being down the right field line, we were able to sneak down and have front row seats for the President's Race. I have a great picture now of the presidents racing right past my kid.
(4) We snuck down to right behind the right field line ballgirl in the hopes of getting a baseball. Nobody hit a foul ball down there while we were in the area and Lane Thomas seemed to prefer to throw his warmup balls into the center field seats. However, a racing president threw my daughter a t-shirt which was the highlight of the game for her.
(5) She was definitely drawn more to the CF scoreboard than to the action. She asked a lot of questions about what various numbers on the scoreboard meant and this was often the start of me explaining things about baseball to her.
As advised, we left at the start of the 8th inning, exited via the Right Field gate, and got in line for Kids Run the Bases early. We were maybe the 4th or 5th family in line and the line eventually got HUGE. The downside is that we missed the epic 9th inning rally where, after being down 7-2, the Nats came back and won the game.
My daughter insisted we time her running the bases and she made it from first to home in 32.5 seconds - she claims she can do better so I guess we'll be back one day to see if we can improve.