dear colleague to be...
I think it is wise to ask the people already working at you new place of employement what their opinion is.
They might have some good suggestions.
In general group therapy is concidered when:
a group of patients/children with the same problems needs to be treated
if you have more than one child with the same type of problems
if you do not have enough time to treat everyone as much as you wish
if you want the child to have some extra treatment as an adjunct to normal therapy
Hopes this helps you a little
kind regards
Esther