Regression is acting younger than you typically act. Trauma and stress can make children feel powerless. Children may regress as a way to find comfort in how things were before the event.
In children aged 2-5 years
Thumb sucking
Asking for a bottle
Wetting the bed after being fully potty-trained
Not showing interest in usual activities
In children aged 6-10 years
Baby talk
Wetting the bed or having toileting accidents
Playing with toddler or baby toys
Pretending to be a baby outside of pretend-play with friends