and here are lots of exercises for basic vocab and grammar as and when/if you get onto it. Not very flashy or exciting but in my previous life my classes of 30 likes it for an hour. Might be a bit "teachy" BUT should be able to work through it at own pace.
Will look at Reading Eggs (don't know what it is ) and see if I can think of anything similar
Linguascope (the expensive one) was good as a teacher, but I'm not sure that it would be all that good for the whole immersion thing. I definitely wouldn't pay £200 for it! I found this French site aimed at teachers, but it has some good resources for songs and you can make puppets and things from them. You do need to trawl through it a bit though.
Momes Net is aimed at French children, but there may be things your children would enjoy doing on there too.