Mad EngineBoy's Goosebumps Logo and Characters Glow-in-the-dark Kids T-shirt T-Shirt

Both size charts are for youth little boy and youth big boy, so which do I go by? Not sure if I need to get my 8 year old a medium or a large?

How long does it take to get the tshirt?

Is the XL a 14/16?

Which size chart is it? The first chart shows small=size 4, and the second says small=size8.