Hi,
My son's pediatric dentist is recommending a w-wire for crossbite.  What I've
read on the topic, there are two schools of thoughts.  One advocates two
phase treatment - orthodontia at a young age, then a second phase during the
teen years.  The other side seems to feel the orthodontia at a young age is
wasted, that you still have to repeat it again later with no diminishment in
time invested.  

I'd be interested in professional thoughts on this.  My son is 4½ and would
be 5 at the age of treatment.  He has no major problems, other than
occasional grinding at night.