You are describing a normal two stage treatment.

Normally, after having a palate-expanding appliance, braces are
necessary to further correct your child's bite.  Expanders are
typically a Phase I treatment, meaning they set your child up for
further treatment later to fix remaining problems with their tooth
positioning, which is typically braces, or Phase II.

Should you feel your child isn't prepared to handle braces (they
certainly do require a certain level of responsibility to ensure they
stay clean and do not break), waiting to put on braces is certainly an
option.  To maintain the space created by the palate expander, a
variety of appliances can be used.  The two most common are the TPA
and the Nance.  The TPA is a trans-palatal arch.  It is a single wire
which lies across the palate and is attached by bands (the metal
rings) to the molars.  A Nance appliance is very similar to a TPA,
except it has a small disk of acrylic at the peak of the archform
across the palate.  Both maintain space.  These can essentially be
left in indefinitely.  I had a Nance appliance in my mouth for six
years, because although I had space, some of my teeth still had not
come in quickly enough.

Working in an orthodontic practice, I know that the number one reason
why kids need braces again is because they have poor compliance with
wearing their retainers.  If a retainer fits a child properly when it
is made, there is absolutely no reason for their teeth to move, should
they wear it as they are told.  Wisdom teeth coming in and turning
teeth cockeyed is a myth; the real culprit is not wearing the
retainer, so that the wisdom teeth have the freedom to move unretained
teeth.  If parents were more proactive about making sure their
children were wearing their retainers properly, fewer children would
need braces a second time.  Additionally, a child must be able to
handle the responsibility of having to wear the retainer.

Fortunately, there are solutions to the problem of children not
wearing their removable retainers.  Semipermanent retainers do exist;
they are thin wires glued to the inside surface of the anterior teeth
(usually lower, however upper retainers are appropriate for some
patients), called bonded lingual retainers.  Kids can't get these out
unless they chip them out with something sharp; normally only the
orthodontist can remove them, and the kids completely forget they're
there.  These are normally used in conjunction with a clear plastic
removable retainer, but if the patient forgets to wear the clear
retainer, they have security against their teeth moving with the
bonded retainer.

Do not be afraid to put braces on your child once the orthodontist
feels it is appropriate.  If you can help make sure your child is
brushing properly and keeping his or her teeth clean, there is nothing
to fear as far as cavities and the teeth not ending up the way they're
supposed to.  The biggest issue, and the one that often is swept under
the rug, is retention, and again, if you can either use a
semipermanent method or ensure your child wears their retainer, he or
she will not need braces again for their entire life, as long as that
retainer fits.

Ashley