A budding mathematician

Me: Are you ready for bed yet?
ER: No
Me: What do you need to do before you're ready for bed then?
ER: Can you please play catch with me?
Me: You need to play catch first, and then you'll be ready to go to bed?
ER: Yeah.

So off we went to her room to play catch with her tennis ball. I discovered that she's become pretty good, with a decent overhand throw. Mama came in and joined and naturally we started passing the ball in a triangle. I started a counting game wherein each of us would count off the next number in sequence as we caught the ball in turn, as such:

Me: One
Mama: Two
ER: Three
Me: Four
Mama: Five
ER: Six
... (Elena kept this up successfully)
ER: Eighteen
Me: Nineteen
Mama: Twenty
ER: Eleventeen

...
Me: That's very good Elena! Good extrapolation! It's not quite correct, but good reasoning nonetheless. Full marks!