They’re experiencing restraint collapse.
You’re doing a great job parenting! It’s one of the most difficult jobs in the world to do well. Restraint collapse is a great indicator that you’re doing well. It’s also hell because you take everything on. Thank you for parenting well.
Off topic: Are his nostrils that vertically different? Did I never notice this during the airing of the show? It looks like his nose is having a stroke in the second image.