Welcome to the forums, and nice find! I haven't seen this before, either.
To me, it looks like properly licensed merchandise related to one of the Lemmings 1 console ports. The lemmings are drawn in the style of Lemmings 1 box art. Even though I haven't seen this particular scene, it is either drawn by one of the original artists or matches that style extremely well.
The red feet (instead of white/beige feet) look like what's printed on the SNES Lemmings 1 cartridge or like the Sega Genesis cover.
The logo comes with the small (TM) in the corner, quite prominently even. That again makes it look more like a licensed shirt, although it's possible that unlicensed shirts would also print that (TM).
I see two dubious parts: First is the misspelling ("Jeronimo" instead of "Geronimo"), but that may well be par for early 90's computer game merchandise. The second dubiousity is that lemmings in this style (with this hairdo, with these eyes) normally don't have the red feet. Covers with red feet typically have differently-drawn lemmings faces.
-- Simon
