It might take a while (months) for him to reengage with the kids if he does, right now his mind is focused on himself only. Most probably his thoughts are very conflicted, in one hand he is getting his freedom something he "dreamed" to have but on the other hand now since you filed for divorce some explanations will have to be given to people when they will ask him or you "why?" and "Is he ready to face others and assume his past actions that destroyed his marriage and de facto the life of his kids?
It's one thing to blame your spouse for your unfaithfulness in the comfort of your own home but saying the same to others who knows you both is a totally different thing.
Do you think that he cares what people will say or think about him?
Me 52+ WH 57+ Married 20 + Piecing since 2016 (ready to give up...)