Teaching my young cousin chess

Start with the basics. Ask the tyke what he thinks he knows and have him show you. How do pieces move? What's check, checkmate, stalemate? What is en passant? Show him castling and explain when you can and cannot. Explain illegal moves. It may take multiple lessons. Be patient! I've been playing for nearly 50 years and am still learning new things about the game. Most of all, have fun!
Teach these basic things.
Two rook against a lone king mate.
Show him tactics like pin, fork, skewer etc.
Show him easy mate problems.
Once you show him these, ask him to try solving easy mate and tactics problems. If he can't solve it in 8 minutes, show him the solution. Use a real chess board here.
Tell him general opening guide lines.
1. Castle to make your king safe
2. Put your rooks on open file
3. Put your bishop on open diagonals
4. Open with 1.e4 or 1.d4
Tell to always study his opponent's last move,look for tactics, look at the whole board and before he makes a move, check if it is a blunder or not.
Once he got better at mates and tactics, make the problems a bit harder. But he should still solve easy problems.
Once he got better at tactics, show/teach him basic strategies. Play with him and try to join chess tournaments.