@Kym Mitchell Did you already plan out your trip to France? There’s a comprehensive itinerary for you  https://www.ricksteves.com/europe/france/itinerary depending on how many days you’ll be staying there or are you interested in getting to know more specifically in Paris https://gowithguide.com/united-kingdom/paris you might consider these resources. You might find it helpful.

You are an absolute Saint!!! Thank you so much for this. We really don't mind hopping from train to train - so those options they have are perfect Thank you @AnnaB 

Exactly the same question was asked by a traveller yesterday. Please read the answers in the link below. 

https://community.eurail.com/routes-destinations-42/last-minute-train-from-rotterdam-to-paris-8841