how to get regular stickers to stick to a t-shirt?

For the 100th day of school, i’m helping my kindergarten nephew make his shirt. he put 100 stickers on his shirt. some are sticking better than others but i’d like for some to last him thru the day! im likely going to use a hair dryer over them to try to melt the glue a lil into the shirt. i don’t think i should iron since the stickers are papery. is there anything else i can (semi quickly) do to improve the longevity of the stickers!?