Could two children, one weighing 30 lbs and one weighing 75 lbs, play on a seesaw together? if so, how could they do it?

In this case, center of mass of the system( 2 kids + seesaw ) would lie near 75 lbs kid.

Note : center of mass lies near particle with more mass.

Children can still play on seesaw if 30 lb kid sits near the edge of seesaw because more torque( Torque = Force x perpendicular distance from the axis of rotation ) will be produced.

More the torque is, less effort kid has to apply.

Hope this helps!

Its a hope this