Circuitry for Running Many Small Motors
It is definitely realistic. Regular DC motors work as follows

1) Speed is roughly proportional to input voltage

2) Torque follows the input current. A higher current gets a higher torque.

1) and 2) are should be under operating limits.

As long as they all have the same behavior with regards to speed and torque, it doesnt really matter if you put them in series or parallel.For above,I recommend in parallel.

Make sure that the battery can source as much current as each motor X 9 safely.Since its for a toy for a kid, I definitely will not suggest a li-po battery, choose a lithium ion battery for that voltage and power combination.