Freemember lasterday?

When my oldest was 2, he would say, "Mom, freemember lasterday when we. . ." Freemember was a cute mispronunciation that we could read more into if we wanted. But lasterday. . . Lasterday is a coined word. Something he made up all by himself. Lasterday referred to sometime before today. Could be yesterday, the day before yesterday, last week or last year. Just lasterday. Great word we thought. Really nice. And the freemember part, like being free to remember was the fun, childlike memory part of it. Freemember lasterday? I just like saying it.
Fast forward 6 years. Our youngest is two. She has an awesome vocabulary. Things aren't funny, they are hilarious! She has been speaking in full sentences (paragraphs, really) since she could put two words together. And she is so little (5th percentile) that it adds to the child savant thing because it's like this little baby doll is saying all these big words in context.
So the other day she says to me, "Mom, may we please go to the park nexterday?" I looked at her. She doesn't even know about lasterday. How did she come up with nexterday? Apparently the word coining thing is genetic. Wow.
"Nexterday?" I ask, wondering if it was a fluke.
"Tomorrow, nexterday. I want to go to the park. Please!!!??" Really big smile accompanies request.
Not a fluke. Nexterday apparently does not mean tomorrow, but any day after tomorrow. So in this way it varies (a bit) from lasterday. Lasterday is any day in the past before today. Nexterday is any day in the future after tomorrow.
Think you can freemember that?