We've just returned from DLP on the Eurostar to Ashford. The snack box contained a fruit drink, two soft rolls, an apple and a chocolate bar. Not sure if you're two year old would eat any of that, my eleven year old wouldn't! There is also a buffet car but I don't know what they sell we didn't use it.
There is a reasonably large area at the end of the carriage for large cases and your pram, smaller cases and hand luggage is placed on overhead racks.
Another good reason for travelling Castle Class is that the carriages are air conditioned. I thought the whole train had air conditioning until speaking to another passenger while checking in at the hotel who complained how hot it had been on the train. With the extremely hot temperatures we had on both journeys it was worth the extra just to keep cool.