Is it normal for boys and girls to sweat when they hold hands? Do I need to see a doctor?

If hand sweating only occurs in that situation and stops when you get out of the situation, it is normal and no medical attention is needed.
This condition is a normal manifestation of a person in a stressful or exciting environment.
And if, in addition to that scenario, sweating is also abundant in a calm state, medical attention may be required.