"Why do cats purr?" Evolved basic social actions, display of affection/assuagement.
"Is it better to boil or bake?" Boil water, bake cake (or get bake).
"Can robots change their mind?" Only if they were programmed with algorithms that enabled them to.
"Why do some things bounce?" Newtonian laws of conservation of momentum, angular momentum and energy.
"Why do spinning balls curve?" The spin of the ball forces air around it in the direction of spin, coupled with a forward motion this produces a difference in air pressures on either side of the ball causing it to 'curve' a path through the air.
I can't help but feel the kids time would be better spent aiming their question at wikipedia instead of another thinly disguised Google Co. marketing site! ;)