First of all children do not need glasses for reading unless the prescription is more than -3.00 diopters or clear vision out to 33 cm. However, if the child read and do schoolwork with glasses less than -3.00 diopters the glasses will make the eyesight worse.
The reason for this is that vision is set for distance. Looking out the window require no accommodation or focusing. When you shift from far to near your eyes will need to accommodate or change focus of -3.00 diopters. So if the child wear -2.00 diopters then the eyes will need to accommodate -3.00 + -2.00 = -5.00 diopters. If the child do this for hours, days, weeks and months the eyes will slowly adapt to become more like -5.00 diopters.
Vision continues to deteriorate at a rate of -1.00 diopter a year.
Apart from the additional stress we also know that the glasses themselves makes the near sight worse. Diverse animal studies shows beyon a shadow of doubt that glasses makes the vision worse.
Is there a natural alternative?
Indeed there is, Magic eyes vision training workshops for children Are the way to go.