Your kids have learned a lot by reading books. I know as a book reader myself that I'll learn words that I've never heard pronounced by anyone. Many times I've been guilty of using a word correctly only to pronounce it improperly.
I wasn't embarrassed because I understand my own limitations well enough to know I was taking a risk to use the word. It is like writing anything in this blog. I don't plan my blog writing or prefer to spend much time on it.
But, it is better to know the proper pronunciation. Nothing can distract from an intelligent conversation more than a glaring mispronunciation. Some people will mistakenly think this is an indicator of education quality.
If you are still your child's main teacher (even if just reading the books aloud) and run across a technical word or foreign word you've never heard before, find out how it's pronounced. When I was reading a book about the human body to my children I think I had to look up pronunciation at least once a page.
If your child has moved onto getting their education primarily through reading, find a way to make sure they are learning pronunciation. Quiz them verbally, have them read aloud to you, schedule them to get some face time with someone who is proficient in the subject.
Scientists names are especially prone to being read wrong since we have so many important scientists from so many countries. The names of specific mathematicians and the theories named after them are in a similar bind. Technical words are often pronounced differently than normal English.
The prompt for this post: I requested a book from the library. When the book comes in, the librarian calls. I came home to find a message on my answering machine, "This is the library. The book you requested...[complete with pauses] ar-chuh-meh-des...The Door of Science is in." The word the librarian couldn't pronounce was Archimedes (ahr-kuh-MEE-deez).
Dictionary.com not only includes the phonetic pronunciation, it also has sound files to listen to. In Ptolemy, the 'P' is silent. Make sure your kids know it!