Do any cabs or uber services have car seats for 4-5 year olds?
Tia
Taxis do not require car seats.
No, normal taxis and ubers do not. A car service (like the one you can arrange for the airport or for longer trips out of town) can often provide one if booked ahead, but not your average taxi.
Your options are - don't use taxis (use public transit or walking), carry a car seat with you, or use taxis without a car seat, just the seat belt. That's up to you.
There is an inflatable booster seat that is somewhat portable, I used it for car rentals when my child was 5-7, but I never carried it around for taxis.
uber aren't taxis.