They are targeting potential Welsh-speakers who are still in the womb, with expectant mums given leaflets espousing the benefits of bilingualism when they go for their first scan.
The Welsh Language Board campaign is up and running in all Welsh hospitals, and is followed through soon after birth. Health visitors checking up on newborns are also giving new mothers a bilingual CD of nursery rhymes and a book of activities to help ensure their baby's first words will be in both English and Welsh.
In some areas, Welsh is introduced to toddlers at bilingual swimming classes. The Assembly government-funded campaign advises parents that bringing their child up bilingually boosts their early development and intelligence, and improves their job prospects in later life.
It also offers advice to English-speaking parents who cannot keep up with their children's Welsh-language skills, arranges one-to-one reading sessions and provides a range of books.
Welsh sporting celebrities, including ex-rugby international Ieuan Evans and paralympian Tanni Grey Thompson, have both backed the scheme, called magu plant yn ddwyiethog (raising children bilingually), or "Twf".
Catrin Saunders, Twf project worker for Cardiff and Caerphilly, said:
"Early indications are that many more parents are opting to bring their children up in both English and Welsh, especially in Cardiff. Some may argue the children are better off learning another modern foreign language, but we live in Wales after all."
Twf claims children who learn two languages "have a head start when reading and counting. They often do better in exams later on".
It also highlights the social benefits for children of being bilingual - such as access to the "treasure troves" of both Welsh and English culture, songs and history.