Check out footage from the end of Kansas City's workout ... as Taylor Swift's boyfriend was heading off the field, he noticed a girl in a "In My RED Era" shirt -- and he just had to thank her for her support with some gifts.

You can see, at first, he tossed one of his gloves to her, but when the connection missed ... he pointed at her and made sure she got his second one.

The girl's aunt, Becky Hardin, wrote on her X page that she and the youngster were thrilled over the interaction.

"I was completely unhinged," Hardin said, "and lost my mind."

Other Chiefs came in to thank the little girl and her family for the support too ... as Hardin said running back Clyde Edwards-Helaire doled out some autographs as well. She called the pair of Chiefs "the best" ... before adding, "Thank you!! You made training camp so fun."