It seems like all you need for a child to start talking in one language is to reinforce another one. This reminds me of a recent post by fellow bloggers at Babelkids. Research has clearly shown that reinforcing majority language skills also improves the minority language skills.
Well, I think LJ has just got down this path. We had a two week break from the playgroup she goes to twice a week (her only regular source of German so far). This week we went back and I was told that she made great progress and started saying quite a few things in German (gleich, Mama - instead of Maman, essen, fertig, etc)! To be fair, I didn't need to be told as I have noticed it too. She said a few things to me in German this week, which never happened before (apart from ja and nein).
On va essen maman [let's go and eat Maman]
Il est ou le Schnecke [where is the snail]
Now, we just need to get her to speak more Portuguese as German will rocket by itself once she starts kindergarten in September!