Cove Moulding. Measure and cut, mitering your ends, the cove moulding, to both soften and strengthen the top of the toy chest. Use 1 1/4″ nails and glue to fasten to the top. Careful about your nails poking through to the insides of the box.
A sample cove moulding is shown here. You can use whatever type of moulding that you want, just remember that the overall thickness needs to be less than or equal to 3/4″