@pettanko @beardalaxy (& tagging in
@sim who criticized the same part of my post)
The kids are apparently 1 and 3 years old. I'm not an expert in neurological development, but from all I know, both should be too young to have developed a deeper relationship with him, so this is unlikely to have a significant direct negative effect on them. Certainly not the baby, and probably neither the toddler, though it may depend on how much negative emotion is carried over to them from other people, like the mother.
As for their future: I don't think growing up without a father in the the household has any inherent negative outcomes. These are most likely to be the result of correlated issues, like households broken by poverty, fighting, and so on. A single mom with lots of money and connections is very different from a single mom who has to work full time with no good connections.
So, without knowing many details about them, I would assume the mother and kids will be financially stable and have a big powerful community supporting them. Those are excellent conditions for growing up healthy. I would expect that the killing of their father will merely be an interesting tale they can tell their peers as they grow older.
But it all depends on the people surrounding them. My main concern would be the risk of the family becoming bitter and vengeful towards "leftists" (or whatever) and one of them eventually continuing the cycle of violence.