For the seesaw to be balanced we need the torques each child apply on the seesaw to be equal, that is:

Where he torque is given by:

where F is the force each child applies and r is the distance from the pivot. For child one we know that it applies its weight, tha ihis mass is 25 kg and the distance is 1.5 m; for child two we know that it applies its weight and the distance is hat we need to find, then we have:

Therefore, the distance from child two from the pivot has to be 1.07 m