Do you practise defending free kicks?

Yes, but I’d keep it short and practical. For a wide free kick, players need a basic picture of who is dealing with the first ball, who is protecting space behind them and who is ready for anything that drops. If you use a wall for a direct central free kick, make sure the players understand who is organising it and what the defenders around it are responsible for. You do not need twenty minutes of set-piece rehearsal. Five minutes in a session every so often, plus restarting training games with real free kicks when they occur, is enough to build familiarity. At U12, I’d rather the players understand the threats than memorise exact starting spots. The ball, the runners and the goal are the important information. The setup should help them deal with those things.