Here's why:
* "Se lo pasaron" means "they spent it" or "they had a good time" depending on the context.
* "En las" is an incomplete phrase. It means "in the" but requires a word to complete it (e.g., "en las calles" - in the streets).
To get an accurate translation, please provide more context. For example:
* What were they spending their time doing?
* Where were they?
Once you provide more information, I can give you a precise translation.