Good Morning Doctor, My Son Is 9 Years Old His

Good morning doctor, My son is 9 years old his weight is 62 lbs he is having itchy and reddish around anus from 3 days and he rubs too much over there, my daughter is 5 years and her weight is 40 lbs she is also feeling the same from today, we have de worming medicine as "Bendex (Alberndazole Oral Suspension) " in home prescribed by the doctor earlier.
can we use the same medicine for both the kids..? or else can we use any other medicine available at OTC ..? i heard about pin-worms from my neighbors, i don't have much idea about it. Please help us on this. your suggestions/advises are much appreciated. thanks in advance.