As a Mom of 2 samll ones (ages 2years and 5 months) the family restrooms are a
big help!  The best ones I have used have an area for changing diapers, with a
comfortable seating spot for nursing moms who unlike me won't nurse in public.
And a seperate bathroom or 2 - the bathrooms should be big enough to have a
stroller and several kids in with Mom or Dad.  My favorite one has 2 "potties"
one adult sized and one of the little kid sized ones - my 2 year old loves that
there is a "Hannah size potty" for her and askes everytime we go into a public
restroom if they'll have a "little potty for me".  Things to consider in the
diaper area - free diapers and/or wipes are useful - can even be left with the
front desk if you find them walking off too often but when you need an extra
diaper this is a godsend!  Easy access to the trash can - can't tell you how
many public reatrooms have a changing table and either no trash can or the
trash can is half way accross the room - not safe to leave your baby on the
table while you throw away the old diaper and difficult to do so once you have
picked up the kid.  One of the best family rest rooms I visit has a sink on the
changing table - table is really an extended counter by the sink, this is nice
as you can wash your hands!  Also difficult to do while holding a baby:)  This
can be a drawback if the last person hasn't wiped up any splashes after they
used the sink - baby might get a bit wet, but then most parents use their own
changing pad and only the pad gets wet.

One potential problem I can see is the waiting for the family restroom might
get a bit long if you have lots of families visiting.  Was at the mall the
other day and there where 4 Mom, 3 or 4 strollers and countless kids in the
Family restroom there - and noone was in the bathroom part, most of them where
changing diapers and nursing.

I think the ones that work best have the bathrooms seperate from the area where
you can nurse and change diapers, just remember that families travel with
strollers and big diaper bags and this area should be able to accodimate them.
Having 2 or more of the double seater bathrooms helps with the waiting problem.

In the Washington DC area the best family restrooms I have used  are at Fair
Oaks mall, Tyson's Galleria and at Ikea.  Many of these restrooms also work
nicely for the handicapped.

Another option to consider is installing a "Diaper Deck" (folding diaper table)
in the handicapped stall as this gives the person changing the diaper some
privacy and takes up less floor space.  Most Moms I know use the handicapped
stall so we can take the stroller in with us - less fear of someone taking your
kid if your kid is in with you.