I have a son who is a keen wicket keeper and when he is up to the stumps to the spinners he struggles when the ball goes down the leg side. Is there any technical advice someone can provide and some drills I could help him with?

Hi Tim, the first thing he needs to do is watch the ball until it bounces so he can get as much information about where it is going as possible. Until it bounces, he won't know the angle or how much it turns etc so if he moves too early, he will get blinded by the batter and be guessing as to where to put his hands. There are a number of ways to do this but a simple one is to hold a pool noodle or floppy stump over him when he is down in his power potion. Tap him lightly on the back and encourage him to stay low the whole time and only move after the ball bounces. Do this with no batter and when he starts to improve then include the distraction of a chair or other object or a batter if you have that person.
Obviously, a low powerful movement sideways is critical as well. The keepers head should stay on the same level and not be bobbing up and down. There are videos on this in the CA Coaches App in the Insiders Tip section. You can download it for free.
Good luck. Enjoy