This is a Birthday gift for my little nephew. (Happy 1st buddy!!!) My sis had mentioned that he didn't have many long sleeve shirts, so here ya go! (This is in addition to the huge box of clothes and toys I'm sending up that my little man has grown out of.)
I grabbed a couple shirts at the store, brought them home and washed them. I usually wash the fabric first if its something that's going to be worn and washed.
I posted a full tutorial on appliquéing clothes here so won't do that again. Will just highlight any differences between cotton and knit.
I opted to use knit material for this set, where I usually use cotton. I like the knit because it doesn't fray, but doing the "m" was a little tricky and the knit wasn't a "firm" as cotton is when cutting and trying to place the applique. The other barely noticeable difference is when I got to the tiny edges (like star points) the knit gets pushed into the shirt with the needle, so you have to be really careful.
Other than that...sewing challenge #35 and #36, check and check.