This scene always breaks me because you see Debbie and Carl seeking Fiona out, going to her for comfort and support, terrified and shocked by what has happened to their mom, needing someone to hold them.
And then there’s Ian who has just bonded with Monica again, spent time with her, had her care for him, talk to him, formed a frail bond with her and then he’s losing her all over again. Ian didn’t want to deal with his mom anymore, after what she did to them, her leaving over and over again but because of he who is he couldn’t help but form a connection with her and had it torn apart.
And he’s seeking out the comfort of the mother figure he still has but then he sees his younger siblings already there and he doesn’t join because he feels like they need it more, that they need Fiona more than he does. But he needs that comfort and soothing touch so much.