Should coaches tell U7s which way they are attacking every restart?

Yes. If they genuinely do not know which goal they are attacking, point them the right way. That is not a football decision worth making them fail at. The ownership we want in 3v3 is around things like whether to pass, dribble, move, defend or shoot. Remembering which of four tiny goals beside three other pitches belongs to you is mostly an organisation issue. I would make it easier as well: consistent bib colours, clear pitch direction and avoid changing ends unless there is a reason. If a child starts dribbling towards the wrong goal, a quick “other way” is enough. No need to stop and teach it. They will become familiar with the setup very quickly if the environment is clear.