I think you underestimate children... Especially those that already knew zwarte piet. Children have anything but shortsighted minds and they will ask questions, believe me!
then its about time Belgians and Dutch owned up to their children and tell them zwarte piet will be changing due to racial history behind the charachter and the time he was created, children can handle the truth!
it's not about putting immigrant WAYS before yours, it's about understanding why YOUR ways might be insulting and disrespectful to the peoples of the old slave colonies of the dutch empire........ surely just a little bit of respect.