UPDATED Thank you everyone for your help with the sleeves.
You may remember that I made these pajama's for my grandson for Christmas? As you can see the sleeves are too short so I am wondering how I fix this? I have serged everything including the cuffs? Do I unpick the serged stitches & maybe add a green cuff or is there a better way to do this. Do I have to undo the sleeve part too? How do I know how big to make the cuff? Should I fold a pc of fabric in half to make it or do I just add a hem to it? I am a bit confused here & could use some help please & thank you