Why is 'play' being used after 'at' here?
The term "play group" is used to mean an organised group providing care and socialization for children under five. It is a common phrase in the United Kingdom and is often used as a noun in the same way as "school", "church" or "work". Therefore "at play group" simply refers to the place that they have been. Ex: I've been at work all day. Ex: I don't want to spend more than a few hours at church. Ex: What did you do today at play group?