It means current English medium schools can still teach English from the age of three, but now have the duty and opportunity to introduce Welsh from age three as well.
Bydd gan ysgolion nad ydynt yn defnyddio addysgeg drochi Cymraeg neu’r Gymraeg yn y blynyddoedd cynnar gyfrifoldeb i gyflwyno'r Gymraeg o 3 oed ymlaen