Using child zip card to Gatwick airport

[Smellycat23]

Hello, does anyone know if my children can use their TFL zip card to get to Gatwick Airport. We're off tomorrow and so I'll need to load money onto their zip card but don't want to do that if I need to buy them a train ticket instead. We live in zone 3 in case that makes any difference. I used my contactless card to get from Gatwick home earlier this year and it was easy but not sure if the zip card will work as well. Thanks!

Gatwick Express - zip card not valid.
Normal rail -valid as far as Coulsden, I think, but not valid to Gatwick beyond that, but you can pay a child fare.

My tfl freedom pass is only valid to east croydon (and not at all on gatwick express), so I have to have a normal ticket for the remainder of the journey.I imagine it is the same for all tfl cards.

Ok. Thanks. I have a family and friends railcard so probably better to use that from Farringdon.