I’d work on dealing with the ball without heading, rather than trying to avoid every aerial ball.
Players can learn to move early, judge the flight, let it bounce when there is space, or use chest, thigh and feet when the ball arrives at a manageable height.
A simple practice is a small game where restarts sometimes come from a longer goalkeeper pass. Let the receiving player solve the flight with pressure nearby.
You can also practise getting the body between opponent and ball if they are waiting for the bounce.
I would not turn it into a line of players controlling high serves.
At U11, the useful learning is reading the flight and choosing a safe legal way to deal with it.
No heading does not mean no aerial football.
