What are the common inflection mistakes that Russian kids make as they progress in mastering their first language?
It's typical of children (of Russian children, at least) to experiment with morphology. Korney Chukovsky wrote a book 'from 2 to 5' about his experience of childern from 2 to 5 understanding the undercurrent rules of Russian. It states such tendencies as
- experimenting (- Дай другую логу! - логу instead of ложку. In fact, why not :) ? But we never say so, of course).
- creating one's own etymology: Паутина (cobweb) -> паукина (as it has a spider, or паук there).
- Widening the semantics: - Облака-то сняли! Сняли с неба облака! (we Russians don't 'take off' clouds from the sky).
I guess that's about it but the examples are fantastic! If you're interested in the book, you can find it on http://www.chukfamily.ru/Kornei/Prosa/Ot2do5/Ot2do5.htm. If you don't understand the Russian there, you can mail me to email@example.com. I've read the book and enjoyed it and I hope that you will enjoy it too!
In fact, as a linguist, I had lectures on children's language. So feel free to torture me with your curiosity :)))