putra = son , son of a king
putri = daughter, daughter of a king.
See KBBI definitions below. (see first entry)
1 anak laki-laki raja; <== son of a king
2 anak kandung;
3 anak laki-laki;
4 khusus (untuk) laki-laki:
1 anak perempuan raja; <== daughter of a king
2 anak perempuan; wanita: -- sejati;
3 khusus (untuk) wanita: lompat tinggi --;
4 cak anak kandung wanita;
"Putra and putri" means "son and daughter", but can also mean "prince and princess", though it more often used to mean "son and daughter". WayangOrang provided the KBBI entries for both words, however, in everyday speech, we usually say "prince and princess" as "pangeran dan (tuan) putri".
While used to mean "son and daughter", "putra and putri" denotes a higher level of respect than "anak laki-laki dan anak perempuan". That's why in everyday speech we just say "anak" to refer to a son or a daughter.