I'm trying to work out whether it'd be beneficial to us or not. The price for a child is showing as £12.99 per day, does this include the same size snack and refillable mug as the adult meal plans, or do they have smaller ones for children?
A snack is a snack, and a refillable mug is a refillable mug.
no difference in size
also consider that there is no difference between a child's QS credit and an adult one, they're all pooled together
some CMs will object charging 4 adults QS credits when there are 2 adults and 2 children listed in the room (example), but some won't
I'm not giving any advice as how to "cheat" the system, but sending one adult with 2 adult meal trays, and the other adult with another set of 2 adults meal trays at the next register ... this does the trick, but don't quote me I'll deny everything
If you're paying for the dining plan then it's very rarely worth it. To many people, the "free" dining isn't worth it anymore either, unless combined with an OKW/SSR room discount.
I'd rather pay OOP for meals than be restricted! That said as we eat a lot of TS meals the DDP works for us (when free!) but QSDP has no real value anymore.