Until they hit 25... insurance is going to be $$$. The 'discount' is having them under one policy.
I've had 5 drivers and 6 vehicles. And the only way I reduced my insurance was to marry them off and have them drop off my insurance one by one (selling/trading in cars I bought for nicer 'married people' cars**)
** It never failed that there would be *SHOCK* when they find out I would not cover them or their new cars on my policy once married 🙂