If they're allergic to chocolate, they are likely allergic to white chocolate as well.
White chocolate chips have stabilizers which makes them more solid and difficult to melt fully, so they don't work well in batters or dough unless you want solid chunks.
The sister of a friend of our younger son is allergic to so many foods it's almost faster to list the things she can eat, mostly fruits and vegetables and not all of those. No meat or fish proteins, no grains, no nuts, no dairy.