Step 1 :We have $10 \text{ km/h}^2 = 10 \times 1000 \text{ m/h}^2 = 10000 \text{ m/h}^2$
Step 2 :We know that $1 \text{ hour} = 3600 \text{ seconds}$, so $10000 \text{ m/h}^2 = 10000 \times (1/3600)^2 \text{ m/s}^2$
Step 3 :So, $10000 \text{ m/h}^2 = 10000 \times (1/3600)^2 \text{ m/s}^2 = 0.07716 \text{ m/s}^2$
Step 4 :Finally, we convert meters to millimeters, $0.07716 \text{ m/s}^2 = 0.07716 \times 1000 \text{ mm/s}^2 = \boxed{77.16} \text{ mm/s}^2$