Expertise

The Sesame Street episode Drew was watching on Boppa's iPad yesterday introduced her to another new word: expert
I asked her what it meant and she said "an expert is when you are really good at something." Well done.
"Ok Drew, what are you an expert at?"
"Cartwheels and bubbles," followed by an example of her cartwheel expertise, which tells me we either need to explain "expert" more clearly, or go back to gymnastics to improve her cartwheels.
"What is Grammy an expert at?"
"Blowing bubbles." Grammy does blow a mean bubble.
"What is Mommy an expert at?"
"Computer gaming." Touche.
"What is Boppa an expert at?"
"Eating pizza."
Clearly she understands the meaning of the word.