T-shirt modification can be done by drawing patterns on it, but of course you can also think of other ways. There is another handmade tutorial by loving mother Oana (see the previous one here), using non-woven fabric to add cute kitten patterns to T-shirts.
Get ready a solid color T-shirt, black non-woven fabric, scissors and needle and thread.
Draw a cat pattern on cardboard and use it as a template to cut the non-woven fabric.
Sew the cut non-woven fabric to the front of the T-shirt with needle and thread.
Embroider the cats nose with pink thread, and embroider the beard and mouth with light gray thread.
Cute childrens T-shirts can be easily transformed. Its really not as difficult as you think!