My son has trouble playing leg side shots. Gets hit on the pads or just misses the ball.
Is it because he’s trying to hit the ball too hard?

Generally, when a batter is missing leg side shots it means their head and shoulders are moving away from the ball. It’s hard to hit a ball on leg stump when your head is moving towards the offside.
If you can get your son moving his feet and head to the line of the ball, he’ll be in a better position to play leg side shots.
Ask him not to try and hit the ball too hard. In the nets get him to focus on keeping his head still, staying in line of the ball and playing defensive shots.
You and he will notice the difference and as his confidence grows so will the runs.
Just because the ball is heading towards his pads doesn’t mean the ball has to be hit for 4. Hitting singles and two’s off his pads is ok and as he gets stronger his natural timing will improve and so will the boundaries.
Here's an excellent video to help

Best of luck

That can be a problem . Most youngsters i have coached actually have their front toe pointed at mid off and have to play around their front pad this drops the back shoulder causing the head to tilt and the eyes are not level. All batsmen need to be balanced at execution which means the head needs to be still and the eyes level.
If you would like to send me a video of your son batting i am very happy to have a look.