My mother in law and I sewed up these Pregnant Twiddle Dum and Twiddle Dee Costume. We bought a monkey pattern and tweeked it a little! We did not add a tail and we made mittens for the hands, then we sewed the feet into the costume. It really did not take us too long.
I found the hats at the dollar tree, actually my 2 year old found it, and I bought two! We just put a paper up to the computer screen and traced the Thing 1 2 letters from a shirt on-line. Then we drew it on the tummy with a black marker.