This is a small Toddler Tee.
This all blue shirt is in baby and toddler sizes only, so it will hardly fit anyone. Which is kind of too bad, because it's cute and colorful. You've got modern jumping-twist Sonic large in the front, standing Knuckles in the back & Tails up high. There's a bit of Green Hill background (but from a more modern game, maybe Generations) & the modern logo at the bottom. Sonic is made to look 'popping out of' the graphic as his foot crosses over the logo obscuring the N.