At play

My girls speak exclusively in gobbeldygook when they play make believe. Is it strange? Is it strange that they understand each other? The only English words they use are pleasantries and titles.
"Ga ba goo da la dee." Then Jennie hands Sophia a pony wrapped in last nights jammies.
"Thank you Miss Gala."
"Bee da ga loo ba doo?"
"Ga la monster goo da lee ga do."
"Help, lava rock!"
"Meeka, you're standing in lava rock!"
Sophia jumps onto the coffee table while protectively clutching her baby, (now a long green block wrapped in an enormous beach towel).

it goes on and on and on...