Justifying the death of civilians implies justifying the death of children, because children are a subgroup of civilians.
Likewise, the ICC bans "intentionally directing attacks against civilians". They do not specify children. Do you suppose that means directing attacks against children is legal according to the ICC? Of course not, because children are a subgroup of civilians.
Finally, I am not your research arm either. You asked me the names of relevant philosophers, I provided them. If you have follow-up questions about their ideas then I applaud your curiousity but you should probably just read what they wrote.
I know you want to pretend that children are not a special class, but there's a reason we treat children differently from adults and the reason that I am specifically talking about then since you are saying their deaths are justifiable.
The death of children is not treated as a special case by the ICC or Geneva conventions. If they are nevertheless protected, then it's not necessary to treat them as a special case.
I understand that you prefer to treat them as a special case, but I don't understand why you expect everyone else to share your preference.