ds has thrush in his mouth and lips

[whoops]

he is 7 and dh is concerned about him getting it from giving him a kiss.
I told him that it shouldn't do but would it?

it depends.
oral thrush can be passed by adults kissing if they kiss in a certain way and for a length of time. if your DH has a weakened immune system either by illness or other medical condition then it may be advisable not to kiss on the lips but on the cheek, forehead etc. your son kissing his dad on the skin will have little effect but on the lips again, as above.
candida is a fungus/yeast rather than a virus so there are different criteria for infection. I think you'll find DS not being able to kiss Dh goodnight etc will have more of an impact than the minimal risk of cross infection. candida lives quite harmlessly in virtually everyone, it is either a pH imbalance, anti biotic, certain diets, medical conditions or a combo of any or all that cause the over growth of candida to cause infections like this. I am assuming your ds has been on anti b's recently, strong ones or for longer than usual?
tell dh to let ds kiss him goodnight on the cheek etc and then if he is that worried, use a baby wipe when ds is out of sight but you are mostly right about infecting.