Giza won't take the whole day, though with two kids, having an afternoon off might be a good idea.
Bear in mind that it can take a couple of hours to get to the airport, so depending on your flight, Saqqara before your flight may be rushed. Traffic is terrible in Cairo.
Khan al khalili might be interesting for shopping, if you're interested in that. The Saladin Citadel of Cairo is worth a stop.
Guides are definitely worthwhile - if for no other reason than the logistics of getting you from place to place with a dedicated driver and watching out for people trying to sell you stuff or scam you.
I used Conde Nast's iconic itineraries to help inspire my trip:
https://www.cntraveler.com/stories/2...luxor-and-more