Thanks for consolidating all the replies you got and posting them; it was
so interesting seeing all the ideas.
As for making your coats of arms, big sheets of poster board give you the
stiffness you need, plus the size some of the kids want. Gluing aluminum
foil, or colored foil, in a few choice places livens them up (the arms,
not the kids ;) ). I tell them they are designing the symbol for their
family and descendents to use for the next 300 years, therefore try to
refrain from incorporating sports teams, a love interest's name, or
gang-type names in their arms, as these things are kind of transient and
wouldn't stand the test of time (kind of like guys who get a new tattoo
with every new girlfriend or wife). Some of my students have chosen to
write a motto in their native language.
Good luck with your classes.