The Greek adjective mikros means small, little, least, or of little account. It describes physical smallness, young age, low social status, or insignificance. In the Gospels, Jesus consistently inverts the world's valuation of mikros — the 'little ones' are objects of divine care, the 'least' are the greatest in the kingdom.
Jesus's repeated concern for mikros — 'little ones' — is a central thread of Kingdom ethics. To 'cause one of these little ones to stumble' is a grave sin warranting millstone judgment (Matthew 18:6). To serve 'the least of these' (elachisto, a superlative form) is to serve Christ himself (Matthew 25:40). The Kingdom's upside-down values make the mikros matter supremely — in God's economy, smallness is not weakness.