The son of a tsar is a "tsarevich" (öàðåâè÷)...
The daughter of a tsar is "tsarevna" (öàðåâíà).
A prince in Russian is a "Knyaz'" (êíÿçü)...
A princess is a "knyaginya" (êíÿãèíèÿ).
(You'll have to set your encoding in your browser's 'View' pulldown to "Cyrillic-Windows" to be able to view the Russian in Cyrillic Russian text).