The kids show "Dora the Explorer" had a pilot episode. It is unknown when this pilot was completed, but as of 2018, Funline Animation, the company that helped produced the pilot, uploaded a short clip of it on their website. There are 2 unaired pilots. A clip of the first pilot can be viewed here. In this pilot, you can see that Dora and her friends went to the beach. The ending of the second has since resurfaced which can be viewed here.
This pilot can be found online, however, the audio (if any exists) is unavailable. Dora has the final design, however, Boots still isn't the same as the final.
EDIT: Pilot has been partially found, an user uploaded it to youtube https://youtu.be/Ib6lGZkwHxg