Shirt: Quiksilver (found it at the Rack but you can buy it here)
Pants: Old Navy cargos (similar here)
Hat: San Diego Padres (similar here)
Little Man's shirt is actually a size 3T (he usually wears 18-24 months), so Quiksilver runs a bit smaller compared to other brands. Their website sells it starting at size 6 months through size 7 for boys. I happened to find it at Nordstrom Rack for a great deal. I love how soft it is and it's been great for layering.
I found his cargo pants a while back in the clearance section at Old Navy (I've been buying larger sizes for him to grow into when I find a good deal). It's hard to see in the picture, but the bottom of the legs actually zip off so they can become shorts too.