I think either works, but "of" is more correct.
Not a grammar nerd, but I view:
"Bob is the parent to Jim" as placing "parent" as a role, e.g. you could say "Bob is the neighbour to Jim", or "Bob is the caretaker to Jim"
"Bob is the parent of Jim" as placing "parent" as a possession, e.g. you could reverse it to "Jim's parent is Bob"