First, it is more important to instil a passion for reading, and its corollary, the English language; than to ensure that a toddler learns more English words for the sake of his knowing more English words.
Second, it is more important for the parent to speak English that is grammatically sound and phonetically accurate, to his child, every day; than to speak in slang, e.g. Singlish, and to use standard English only during ‘teaching’ sessions. Children learn by imitation and even adults learn a new language more effectively by immersing themselves in a culture or society that uses that language. But if the people around them speak the language poorly, that is what the adult learner will pick up. It is therefore not surprising that Singaporeans in general do not speak, and write, English well. English language teachers in the primary schools are not setting the right ‘linguistic’ example by their poor speech habits.
Third, it is more effective for the parent to insert a ‘difficult’ word every now and then in his conversations with the child than to set a specific session for the learning of new words. I do this often with my children and they will tell me that they do not understand this word or that word and it becomes a teaching moment on the spot.
That said, I am neither discouraging the use of Singlish in my case nor claiming that slang is a sub-standard form of English. No, Singlish is a non-standard variant of English, not sub-standard. It is all right for Singaporeans to speak our unique slang among family members and friends. The problem is, we are also parents, and we want to teach our children standard English. The best way to do so is to avoid using non-standard forms in the home at all times. Children will have their classmates with whom to get acquainted with their local slang.