Toddler cardis run very big. When we release new ones the sizing will be much smaller. They are 2-3 sizes big before washing and 1-2 sizes big after washing. My recommendation is to purchase 1 size smaller than he is currently wearing for a loose fit, and 2 sizes bigger for a more slim fit, or just plan to have him grow into it.
Mint cardis are an open style - no buttons or any way to close them.