Tennis for kids is NOT the same as for grown ups, mainly because.....children ARE NOT mini adults!!
There are major differences in terms of strength, speed, agility, co-ordination, endurance etc to make it a different game.
That's not to say that there are not similar aspects, but to teach a child in the same way as you would teach an adult is not going to bring the best out in them.
So the right tennis drills for children are important to "set the stage" for them to grow into the game.
Here are 2 videos that you should look at.
This first video shows an early but important drill/progression for the young player
This second video highlights the importance of the correct drills progression