I know the area very well. There are lots of kid/bump friendly places a short walk from the station. I've listed some below in case we want to pick somewhere (then people won't have to worry about being a little late) but equally happy to meet at costa in the station. Thoughts?
Crumpet (Northcote Rd) - baby/toddler friendly cafe, best for light snacks, coffee and cake
Strada (Battersea rise) - better if we want a proper meal
Giraffe (Battersea rise) - another kid friendly chain. Range of meals from soup to burgers to stir fry vag/chicken.
Banana Leaf (Battersea rise, near cnr of Northcote rd) - cheap and cheerful asian. Noodle soups, curry, rice dishes.
Buona Sera (Northcote road) - nice italian which is often noisy so our chats/children noise will go unnoticed
There is also a Starbucks on Northcote rd with plenty of space for bumps/pushchairs
There are many more places along Northcote rd and Battersea rise but I think the ones I've listed are probably best for groups and are also not too far from the station.
Northcote rd is about a ten minute waddle from the front of clapham junction station and Battersea rise is about the same. There are also buses (319 along Northcote rd) and 35 or 37 up to Battersea rise for those for who waddling has become annoying.