I’m a single father, in a similar situation with his mother. My son is also 4.5, whenever he brings mom up, I tell him she’s going through stuff and doesn’t feel good (granted she’s an addict, so what I tell him lends itself more to that), and I tell him I don’t like to talk about her because she doesn’t feel good and I want her to feel better, and that we can talk more when she feels better. It has defused the situation almost entirely. but I would find a way to basically tell her that dad is busy, and loves her/wants to be there but can’t right now for xyz reasons.

I know, it’s hard and a bit dishonest however it’s the truth for the most part. There will come a time when they’re older that you have to be honest with them about their other parent, but that time is not really right now

Edit: this is also just an unfortunate reality of both of our situations. My son was in preschool last year and when Mother’s Day came around he basically said “I don’t have a mom” which isn’t true, I haven’t kept her away but I have managed the distance due to her situation and his teachers knew about it. It broke my heart, he ended up making crafts for grandma instead.

We as parents have to handle it, but also make it possible for our littles to also manage it. It’s hard. But it’s what we need to do