My family has visited DLR over Thanksgiving weekend for the past five years, and dined at the Thanksgiving Feast for the past four. Historically, there have not been any special events or parades in the Parks for Thanksgiving. This year, you can expect Paint the Night and probably Disneyland Forever to run at Disneyland and World of Color to run at California Adventure.
One way to answer your question is to ask yourself, when does your family enjoy a Thanksgiving meal if you were celebrating at home?
We've always made reservations for the latest seating available (this year it's 4:45 PM) because we like the idea of having our Thanksgiving dinner at the Feast. The ballroom is always beautifully decorated and the food is traditional (heavy) holiday food. I personally think getting rides and other activities out of the way earlier in the day helps to work up an appetite. After the Feast, you may not feel like moving too much and taking in a nighttime show has always been a perfect way to end the day. If the Feast doesn't fall too far behind its seating times, you should be able to get out in time for the nighttime shows in either Park.