Use the space the rule gives you. Roll or throw the ball out to a defender, get angles either side of the keeper, receive on the half-turn, and carry or pass the ball past the build-out line under the press that follows.
Mark the build-out line midway between the top of the box and halfway. When the keeper has the ball, the opposition retreats behind it until the ball is in play (a second player touches it or it crosses the line). The keeper rolls or throws to a defender, never punts. Defenders spread wide, a midfielder drops in, and the team plays out and past the line. Once it is live, the press is live too.
Few rules in youth football exist to teach something rather than to regulate it. The build-out line does. The opposition must retreat behind it at a goal kick or a keeper's possession, which manufactures a moment of genuine space that would never occur naturally, specifically so that young teams can practise playing out without being punished for it. Most teams then waste it by hoofing the ball long anyway.
Using it starts with the defenders' positions. They split wide and high enough to give the keeper an actual angle, which feels uncomfortably far apart to a nine-year-old and is the point. Two defenders standing near the posts give the keeper nothing but a straight ball down the middle.
Roll or throw it rather than kicking it. Accuracy matters more than distance here and a rolled ball is easier to control, and it should go to the defender's back foot so he can open up and face the pitch instead of receiving square with the touchline behind him.
A third option is what stops it becoming a two-player exercise. One midfielder drops in, so the keeper has three choices rather than two, and the pressing team cannot cover them all when they arrive.
The part to rehearse is what happens as the press arrives, because the space evaporates the instant the ball crosses the line. Players should already know whether they are carrying or passing before the first touch, since deciding afterwards means deciding while somebody is running at them.
Worth telling players plainly: the rule gives you a few seconds nobody else in football gets. Use them.
Save it to your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block. Or start from a blank pitch and build your own.