At the outset I noticed that there were more kids, than I expected, that did not know how to play chess and some that knew the basic moves but not simple opening tactics. The purpose of this post is to provide tips for these students.
It is a long way between the beginning of a chess game and the trapping of the opponent’s King. At the start Developing pieces (Knights first), into the middle & King safety (ie look to castle) are key.
My advice is to stick to a particular opening for the first umpteen games and see what you can learn from practice & books (or even the internet). When I was playing chess at school I switched to the Caro Kann defence (a fave of Bobby Fischer) as few opponents had come across it.