most kids who stay with tennis through puberty and beyond in my experience either get friends to play with them or make friends within the club/facility they are playing.
fun is very important,
developing a positive self-image as a tennis player
give them a good technical foundation to build on.
to make them good competitors and enjoy the pressure of matches, praise them on their ability to work and train hard and improve.
donīt necessarily praise talent or results.
if you praise them on their work ethic they will train harder.
if you praise them on talent and results, the danger is that they will find it difficult to play against better players for fear of losing and therefore losing their self-image as talented.