This is my second year umpiring Little League. Last year, I know I had too tight of a strike zone for the 9&10yo's. This year, opening day, I opened it way up from top to bottom, from side to side. The other umpires seemed to follow and we had huge strike zones.
Now that we're over half way through the season, I've tighten up a bit. Last night I called a game where even though I was behind the plate, I was basically a base umpire. EVERY kid that came to plate laid off the bad pitches and swung at everything close. I think I had 5 called strikes on the night. Kids were swinging, the ball was in play and we played 5 full inning in under an 1.5 hours.
Both coaches told me what an outstanding job I did. I smiled and said "nope, I didn't do anything. Your players swung at the good pitches, laid off the bad pitches. I was just a spectator".
Last year I got roped into calling a championship game for 8yo's. My strike zone was chin to below the knees and 2 to 3 balls on either side. In between innings I had a coach tell me my strike zone was too small
My advice to you calling 9yo's is, shoulders to anything low that the catcher can catch without the ball hitting the dirt, either side of the plate where the catcher can catch it without lunging, and move the plate with each batter. Try to find the strikes and if the kid has the bat on his shoulder with 2 strikes, anything hittable is a strike.