Your mistake is that you were counting the children who left the bus rather than the children who remained. Look carefully here:
When bus left the school, x children were in the bus.
When bus reached the first stop, x - 4 children remained in the bus
When bus reached the second stop, (1/4)(x-4) left and (3/4)(x-4) remained.
When bus reached that third stop, (3/4)(x-4) - 10 remained.
(3/4)(x-4) - 10 = 14
Solve for x and we're done.