Four years ago I mused about possible second languages for Helen and mentioned that I had tried talking to her a bit in German. And German is the language we've progressed most with, though sadly not very far.
The extent of her knowledge is the numbers, assorted colours, the months of the year and various animals, and a few verbs. She still gets excited by the mildly different orthography, sometimes breaking into a chant of "umelaut! umelaut! umelaut!". She's proud of being able to count in German and will start doing so at the drop of a hat (to twenty, and perhaps now one hundred). And she sings along to German songs from her books ("Oma hat heute Geburtstag") or YouTube. So she really loves what she's done so far, which is great, but in a way that makes me feel worse about never having organised any kind of tutoring for her, or any exposure to a native speaker.
We used some of the DinoLingo materials, though I found their videos a bit annoying. The biggest success (perhaps reflecting my own prejudices) has been with the Hueber "Spielerisch Deutsch Lernen" series. Helen is proud of having these books, but has only recently got the concentration to go through them systematically. So we're doing that now, with her reward when we finish being the next level (Lernstufe 1) books.
There's a German Saturday school in Summertown, which looks great, but unfortunately clashes with Oxford Youth Choir rehearsals.
Helen's also done a tiny bit of Latin, starting after our visit to Hadrian's Wall, using the Minimus books.