We can use the equation $t = \frac{v}{g}$, where $v$ is the initial velocity and $g$ is the acceleration due to gravity.
For child A, we have $t_1 = \frac{v_1}{g} = \frac{70 \text{ ft/sec}}{32.2 \text{ ft/sec}^2} \approx 2.17 \text{ sec}$.
For child B, we have
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