Would this have worked if both parents were frantic to see Kevin?
It's written that the dad is emotionally detached. He's happy to look after the other kids while his wife drops everything and tries to fly home.
When he finally sees Kevin just gives him a hug and is like 'ah Kevin' and moves on, then says 'what a funny little guy' instead of 'I'm proud of you son' when he finds out he had bought milk.
Having him detached allows the focus to be on the mother-son relationship which was fractured slightly.
But could they have written it that both mom and dad want to see Kevin?