How often should U12s practise penalties?

I’d practise them occasionally, especially if you are playing cup football, but I would keep it a very small part of training. Penalties can be useful for striking technique, routine and dealing with a bit of pressure. You can easily include five minutes at the end of a session rather than building a full practice around them. I would also let different players take them. At U12, I would not create a permanent penalty taker too early unless the group naturally wants that. One useful idea is to let players choose where they want to place it before they run up and then judge the quality of the decision and contact rather than just whether it went in. The shootout moment can be emotional, but the technical action is simple. A little familiarity helps. Rehearsing it every week is not necessary.