The commonest cause for white spot on the side f his cheek could be worm infestation. Give him a single dose of deworming medicine like Albendazole
10ml at bed time.
deficiencies are the other causes. Give him adequate and healthy nutrition. You can also try giving him syrup like Zincovit
5ml every day.
The sore inside the cheek most probably seems like an aphthous ulcer. This should also go away with adequate nutrition and syrup zincovit in 3 weeks time.
If it is not all these, then it can also be superficial fungal infection
If the above measures fail, see a Dermatologist
for clinical evaluation.