http://www.mcsl.org/documents/rlyorder.html Here’s the list of events at relay carnival. If your swimmer has not swam at any A meets it is very unlikely they will go the “Divisonal”/A carnival. Some pools may have a B carnival that they participate in with other local pools.
At a division B pool your child will need to be quite fast to compete. For the younger kids the options are the gender medley relay, mixed freestyle relay and then the three events that take swimmers from different ages - the crescendo freestyle, the graduated medley, and the graduated freestyle (this last one is also swum at the conclusion of A meets)
For a not top swimmer your bet is going to be to get the kid to the #2 or 3 spot in one of the more technical strokes (breast/butterfly) and then assume the faster kids will take the other spots in the age /gender specific medley.
Basically for 8U girls (example) there’s one event with two freestyle spots(mixed freestyle) three events with one freestyle spot (assuming pools usually stick the 8U in freestyle for the graduated medley), and then one event with one of each stroke.
Division N poster - your carnival lineup has already been sent to parents? And I’m assuming yours is actually Sunday July 9 not Saturday?