Are children more susceptible to pinworm?

Yes and no: I guess, you can look at this from 2 different angles. The "yes" angle is that their hygiene is not as good as that of adults (not universally true...), so they are more prone to contract pinworms than adults would. There is nothing wrong in their immune system, though, that makes them more prone to acquiring it and that's the "no" angle.

See below: No, children do not have an increased susceptibility.

They are more likely: To have symptoms from the nematode.