If there was no spring it would need some other kind of energy storage device. For example, a pendulum clock uses the potential energy of the pendulum in order to store the clocks energy. This is probably not the case in a toy, but it still needs an energy storage system.
Stretching a strong spring requires more work because it has a higher spring constant, meaning it resists deformation more than a weak spring. The work done in stretching a spring is directly proportional to the square of the distance it is stretched, so a strong spring will require more work to stretch the same distance as a weak spring.
The equation for the work done by a spring is W 0.5 k x2, where W is the work done, k is the spring constant, and x is the displacement from the equilibrium position.
The work done by a spring when it is compressed or stretched is the energy stored in the spring due to the deformation. This energy is potential energy that can be released when the spring returns to its original shape.
The work done by the stretching body is equal to the difference in potential energy stored in the spring before and after it is stretched. This work is done against the restoring force of the spring.
The formula for calculating the work done by a spring is W 0.5 k (x2), where W is the work done, k is the spring constant, and x is the displacement from the equilibrium position.