My son just got treated from hfmd; however, the virus was transferred to his cousin who is showing symptoms of hfmd already. can my son re-contact it?

Probably not...: HFMD mostly affects infants and children younger than 5 years old. However, older children and adults can get it, too. When someone gets HFMD, they develop immunity to the specific virus that caused their infection. However, because HFMD is caused by several different viruses, people can get the disease again. (From the US CDC website)