My son is finally ready for school at 18 months! Where can I buy a backpack for a toddler and any recommendations on brands you liked?

What kind of school is he going? Childcare or just those 2 hrs playgroup? If its full day childcare then get those trolley bag so that he can pull along and wont be too heavy for him to carry. If its just 2 hr playgroup then get him a small haversack. Most important is to get him a bag with a character that he likes. Usually i bring my boy along and show him a few suitable option and let him choose