These, so far, along with names, are add-ons for uniforms provided by the area Little Leagues and similar youth programs, and done for individual teams.
Interestingly, in a fifteen mile radius, I see at least four separate Little Leagues and two independent just for the younger kids.
When my son participated in our local Little League, they re-used jerseys so adding names was not even an option though I often added names to teams from other league shirts.
A few years ago, our league began handing out "keepers" but, ironically would not allow names! Seems that they were concerned with facilitating child molestation
with an easier way to feign familiarity by using a youngster's name.
I know that more than once, I saw a different name in his hat and wish that I had done at least this part of the package back then.