"These are my son and daughter."
Translation:Ini putra dan putri saya.
Jake is correct and incorrect. If the son and daughter are introduced as one thing, the subject is singular. E.g ham and cheese is my favourite filling Vs. ham and cheese are my favourite fillings. The first is singular; the second is plural. In the case of a son and daughter using 'these' sound better and avoids arguments about grammar; however, which should be used would depend upon the context. If showing a photo, I would use the singular. If pointing to them, I would use the plural. You simply decide if they represent a group or two nouns.