Birthday Party

For my brother Matthew's birthday lunch Teddy wore a Janie and Jack Winter Walrus shirt I got at a consignment store(50% off!) and Gap khaki cords.  The shirt is size 0-6 months.  I think that's such a bizzare size.  What item will fit a baby from newborn to 6 months?  It's still a little big on him.

I put Tillie in a dress that was mine as a little girl before lunch just to take her picture.  She didn't want to take it off before we went to my brothers' house.  "Grandma will LUB it."  Sizes used to be a lot more inaccurate.  This dress is a 4 and is SUPER-short.