Dalia,

      I wish I were a fairy would be a version that acknowledges
subjunctive mood. It seems to be disappearing from the language, so that
at this point in time both forms would be common enough to be
acceptable.  I tend to vote for it in practice (I use it), but not
insist on it too heavily. I have no idea when the subjunctive would be
age appropriate.
     When I give the statement from my son to my classes, it's not to
show that he is very advanced for his age, but to show what a somewhat
typical five year old is capable of.  Our students need to learn a deep
respect for the complexity of our unconscious grammar.  I gave it again
here just as first hand evidence that children this age use subordinate
clauses routinely.  I'm not an expert in language acquisition, but I do
know that content clauses and adverbial subordinate clauses come very
early.  When my adult grammar students analyze y son's sentence, they
gain respect for the complexity of the clause relationships in a young
child's natural speech. Students who are parents often bring in examples
of their own. This is a priceless understanding, perhaps more important
than anything else I teach.
     Whenever we teach grammar, we are somewhat forced into isolating
language from all kinds of contexts.  I like the idea that you teach the
parts as part of a whole.  Most ESL grammars seem naturally functional,
since learning a language is learning to function within its community
of users.  You also have a need to be systemic, since you can't get away
with teaching the parts of the language that native speakers sometimes
have trouble with, as many traditional grammars do.  Your students  need
to learn the aspects of language that native speakers can and do take
for granted.  I suspect that's why you have gravitated toward a
comprehensive approach.  I'm glad that it's working.