If something need to improve, pls use positive tone.

If you see the improvement, pls mention it and encourage more improvement.  no need to lie. don't be too silient. because you would have worked there for 1 month at next meeting.

 

for 2nd point, no need to explain, no need to invite for lunch. It will remind them what you said. Take it easy, and smile to them, appreciate them from heart during this month.