Many children get overwhelmed during the holidays. They cannot manage the change of routine from daily school to the many facets of travelling to see friends and relatives, or just a bustling home life filled with the excitement of the season. If they have siblings who are extra loud, excitable or mobile it can be worse.
Some parents dread the holidays because their child becomes more reclusive or acts out more. Some parents get frustrated because their child won't try new things (or wont' engage with others), and/or becomes defensive with smells or sounds that have increased due to baking, music, or more people in the home.
Sensory processing deficits are very real for the child experiencing them. They cannot always organize themselves to manage the changes of the season. The visual overload is enough to send them running, and there might be confusion with expectations and a loss of sense of time. I found the article below to be helpful (click on it). The most important facet of success is knowing your child and preparing in advance for any possible areas he/she may be triggered or reactive. Being prepared with toys that work to settle your child, having an exit strategy (or place they can go to reset when overloaded), and preparing your child for what he/she might expect are paramount for a successful holiday gathering. 7 ideas to help children with SPD through the holidays season (griffinot.com)