use, yose, have yosen

I have experienced a strange phenomenon. (So what's new?) My kids have invented some interesting words and use them in place of what is conventional. One that just about everyone said as a toddler was "amn't." This is short for "am not" and was used mostly in the phrase, "amn't I?" I only noticed this because my mom told me I used to say the same thing when I was little. Elizabeth has gone a step further with odd contractions and has added "willn't" to her vocabulary. This, of course, is short for "will not," and takes the place of "won't." Actually, hers makes more sense. The one that by far bugs me the most, however, is the verb, "to use." "Use" is a regular verb. It doesn't get any simpler than this: use--used--have used. Apparently this was just not complicated enough for my kids, because they have changed it to a highly irregular verb and conjugate it thus: use--yose--have yosen. What is up with that?