Want to make a sequel with a great character but already killed 'em, don't own the rights, showed up 20 years too late, or simply have no imagination? Just sequelize the family! Sons, daughters, nephews, nieces, convenient identical twins, second cousins twice removed, or even prequelized forebears!
More recently, bigger franchises have teamed generations up to try to appeal to new and old fans and prolong the magic.
It's probably not a coincidence that some of the movies on this list are crap (certainly not all!). Additional suggestions welcome.