They will let you take a light stroller up to the gate and at that point this will be put in the hold. You will likely be expected to fold it yourself.
Re the car seat, are you certain that it is completely suitable for use at your destination?. Also such things can be damaged by baggage handlers, at the very least it will need to be well packed. That will be put in the hold when you check in.
(If you happen to be departing from T5 just ensure you give yourselves plenty of time to get to the gates. Going to B and C gates will entail a ride on the transit train and a longish walk once you get off this. T5 also has family security lines; you should be directed to one of those).
Do not rely on them to fully provide re food; take foodstuffs that you both like to eat and a change of clothes for you both.
Hi, am flying longhaul with DS in December with BA and would appreciate advice re strollers vs travel system. I am traveling alone with him, he will be 4.5 months but is a big boy so too heavy for sling all the time and have 2 connections, plus woukd like him to sleep at some point and he wont in the sling. Does anyone know if you can take a heavier style travel system buggy to the gate or if it must be checked with luggage? If need be I would buy a maclaren stroller to use and leave travel system buggy at home and check car seat. Advice / suggestions appreciated, many thanks!