How does the coach decide which swimmers to place on a relay team?
There may be exceptions, but generally, the swimmers are chosen for relays based on their seed times. For example, for the girls 9-10 200 free relay, the four 9-10 year old girls with the fastest 50 free seed times will be chosen for the relay team. If there are nine or more girl swimmers aged 9-10 signed up for the meet, a second relay team will be created, using the swimmers with the 5th through 8th best seed times.