Your parents' wedding anniversary is a memorable day. After all, you are born because of this day. Although your parents want to be more private, your surprise will make them very happy. Here are some suggestions:
First, you can give them a commemorative gift. You can order a crystal product with your blessing on it and put it in their bedroom. They will be very happy with your blessing.
Second, give them a home decoration. After all, they have your family now. You can give them a beautiful table lamp, a pair of beautiful vases, or even a painting.
Third, if you want to give a creative gift, you can make a set of real dolls of the whole family. The realistic and lovely image will surely make your parents love it. It must be very happy to see the whole family together every day. You can also give them a crystal music box. It is very beautiful and has good music. It is also good to put it at home.