I’d encourage all young players to develop a ‘long smash’
One that is hit hard and fast hit towards the rear court
Only practising a smash that lands in the midcourt can be tactically limiting for young players
Accuracy at a young age can be variable so often ‘down’ smashes land closer to the opponent, therefore making it easier for them to cross block.
I recommend that you create practice situations that encourage both steep smashes and long smashes, especially down the opponents backhand side.
If they are hit hard and long, they may resemble flat clears. This is not a problem and should be encouraged 🙂