If one child boards and one is a day pupil, a two-bedroom furnished apartment on Ngong Road often beats a four-bedroom in Karen on both cost and commute. Ask about mid-term flexibility in the lease.
For this audience the single most important specification is gated community living. The gated estate is the dominant residential format in Nairobi's family suburbs. Beyond security, it buys you a road nobody speeds on, children who can cycle, shared borehole and generator infrastructure, and neighbours who will accept a parcel for you. It also buys you estate rules and a service charge you do not control.