Eugene van der Pijll
Adoptive parents reads "When you take a 'Family Growth' Action..."
The Wet Nurse grows your family when you build rooms, therefore you are not using a "Family Growth" action and thus cannot use the Adoptive Parents with it.
How does it follow that you are not using a "Family Growth" action? You aren't using a "Family Growth" action space. There are lots of cards that let you do an action (baking bread, sowing, family growth) without using an action space.
(Actually, the German card Adoptiveltern doesn't even read "Family Growth action", it reads "family growth".)
I'm not sure about the others. For example, the following scenario:
Have Mother of Twins and Adoptive Parents in play. Take Family Growth. Use Mother of Twins to get 2 new family members. Use Adoptive parents to put the offspring into your house (available for use this turn).
Are both new family members available for use this turn?
Does it cost 2 food instead of 1 to use the Adoptive parents (since you are "adopting" 2 children)?
Good question. Reading the Mother of Twins carefully, it seems to say you pay 1 food per child. (German version again)