Currently in a first floor flat with 2 & 3 year old Dds- no garden, one flight of stairs but the ups and downs are horrendous- I had the option of a house but thought it wouldn't be a problem, the flat is lovely, but has been completely impractical- I'd give anything to be able to just get the kids ready and walk straight out of the door!
Example- Buggy down, back up for Dd2, back down to put in buggy (hopefully with no kick offs, or unexpected poo...that happened more than once!) back up for Dd1 & change bag, lock up, back downstairs- then out...
Back, usually with shopping....Upstairs with Dd1, back down, upstairs with shopping, back down, upstairs with Dd2, back down, upstairs with buggy....
Your ages are more manageable but I'm currently househunting like mad (I'm South also, prices are through the roof, so can understand your reasoning) -
I loved this flat, the area given the city is okay, access to decent schools and thought this wouldn't be a problem but with lockdown, no outdoor access, play areas, soft play, groups non existent we've been so isolated- and just on top of each other here- having to avoid people coming and going (8 flats in my block) plus constant deliveries, neighbour noise, car park mayhem....go with the house!