Do you practise free kicks or just play them?

I would touch on it without turning it into a routine. A free kick gives the players a useful decision: can we go quickly, is there a teammate free, is a shot realistic, what space has the defending team left? You can recreate that in training by occasionally restarting a game with a free kick in different areas. Then give the players a few seconds to decide what they want to do rather than calling the answer. I would also make sure different players take them. The value at U9 is recognising the restart picture, not learning a choreographed movement. So yes, practise the moment. I just would not remove all the uncertainty that makes it worth learning from in the first place.