Fantasy/ sci fiction trilogy

[Kyton]

the book is about kids after these aliens have taken over earth and turn it to a farming world and these 3 legged striders like watch over them. the kids find ruined cities and carrages with nothing that pulles it. the kids find gernades in a old subway station. i remeber it was a trilogy but never got around to reading the other books

 

[Occlith]

Is it this?

 

[Kyton]

yes i think it is

 

[Jemima Aslana]

Sounds likely to me. I read it ages ago and wrote a paper on it. I remember I thought they were good.