Bilingualism in Preschool

Why introduce second language in Singapore's Preschool?

Singapore being a multi-cultural country, it is important to maintain ethnic diversity and identity. 
Children begin learning second language during formal schooling (Quentin, L. D., 2003).

This policy is aligned with belief about children’s critical/sensitive period of language acquisition. After the sensitive period, learners may find difficulty in picking-up language at native-level proficiency (Quentin, L. D.,2003). If so, how can we better help preschoolers to acquire these skills?