dear Ansam,
It is not easy to give you an answer to your question, because we cannot see and observe the child you are treating.
How old is the child? Is he or she mentally able? I do not understand, does the child have CP or PKU?
I suggest you go to SfA Resources for Parents, Teachers and Therapists | skillsforaction.com site.
On this site you will find a lot of information and practical ideas.
You can also check this forum carefully. I suggest you look at all the mails in the paediatric section.
The problem you address has been spoken of before. Maybe you can read the posts and that will help you as well.
kind regards
Esther