When our grandson was this age we did Pirates. I made the little guy a line green fuzzy one piece outfit that had a hood. I used craft foam to make the beak and eyes, he was the parrot on hubby's shoulder. It was easy to do since he didn't walk yet.
The girl was the "damsel in distress" so she basically go to dress up like a princess. I wore a long skirt that I made in about 15 minutes. It was 2 long pieces of cloth sewn on the raw edges. The selvages were sewn into a hem across the bottom and elastic tube across the top. I used just the largest white shirt from hubby's closet and tucked it in. I wore boots that I could walk in and not struggle. Then I put a square of cloth over my hair like a bandanna. I had a wide belt from back in the 80's or something and that was a good look with everything else. It made my waist look much smaller.
Hubby borrowed a cotton pull over shirt that my friends hubby wears with his kilt for Renaissance festivals. It has the string ties at the neck with the big sleeves that are gathered at the bottom. He work his black pants and his black work boots. Then he wore just a length of fabric tied around his hips like a sash, and he wore a pirate hat we bought somewhere like a Party supply place.
Little guys costume was made off the view of the bottom right yellow and green bird. I didn't add the scalloped edges on the bottom of the sleeve though. I thought it would be in his way too much. I just turned it up and sewed it in a hem.
http://sewing.patternreview.com/cgi-bin/patterns/sewingpa...
Here are some links to make a parrot costume out of items you may already have too.
http://www.ehow.com/how_###-###-####_make-parrot-costume....
http://www.ehow.com/way_###-###-####_homemade-parrot-cost...
Here's one that might inspire you to create a family of pirates from items you may already have too.
http://www.dresslikeapirate.com/
I hope you get a lot of fun ideas!