Parties essentially bother child: it's rejecting all outsiders, fully (2,3,4)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Middle letter (essentially) of [par] T [ies], then [b] OTHE [r] [c] HIL [d] [i] T [s] with all the outside letters dropped. As in “I’ll back you to the hilt” = I’ll support you fully.