Hello and welcome to e health forum.
Worm infestation is a very common problem in pediatric age group, and it can persist inspite of treatment in many cases.
This is due to the fact that, parasitic organisms have varying forms of life stages, and latent forms can develop even after treatment, as such medications do not affect the latent forms.
The best way to deal with this situation, is to confirm that the stools are cleared of parasites, by a stool examination, done 1 week after the treatment is completed.
In case of persistent infestation, the treatment must be repeated. You might consult with a pediatrician for further advice and treatment.