The world today is so diverse, it is important to accept all people, no matter how different they are. Your child will meet diversity wherever it goes so it’s good that it becomes open to embrace people and practices which are different.
In order to teach your kid how to be open-minded, the most important thing is to check your own openness towards things and people which are different from you.
Your child will mostly learn from your example, so if you are open-minded, your child will understand your approach as a normal thing and it will follow your steps.
So, treat diversity and the differences with respect, treat people equally and don’t judge others if they have the beliefs which are different from yours. Your child will see how you treat other people and it will try to do the same thing.
Of course, your child must understand that the tolerance has its limits as it shouldn’t tolerate the violence towards the people who have a different skin color or have different religious beliefs.
All in all, educate your kids and educate yourself. The knowledge is the key if you want to understand the people who are different from you.