You may pay attention to the following tips.
Firstly, try your best to make your child know the reason why he need to wear glasses and let him know the benefit of the glasses.
Secondly, give your child the freedom to choose the frame he like.
Thirdly, make sure choose a pair of glasses that fit your child properly, neither too tight nor too loose.
Fourthly, offer some rewards for them to wear glasses.
What's more, make it clear to your child that certain activities require glasses like reading books or watching TV.
At last, clean the lenses regularly to make sure that your child feel the glasses are a necessary thing for him to see clearly.