I've used Anki and liked it- I have it on my phone, and I've found it helpful to refresh while I have some time to spare like waiting in a line (anytime you'd usually be playing some game on your phone).
For your kid (and you and wifey) I would also recommend cartoons and kids shows- usually the language in these is a little bit slower, and simpler, and yet uses a natural casual speech pattern- as opposed to something like Muzzy or lessons that are specifically to teach you the language. Muzzy's great but every one talks like they are reading out of a text book ("I am pretty. I am mean. I am the king. I am Muzzy. This is our castle." etc), while a cartoon will read more like how normal people talk every day.
You could probably try buying German elementary primer books online, just like they have workbooks for elementary school children here.