In the '70s and early '80s, there were a number of very young kids who were running marathons and getting a lot of attention for it. Offhand, I remember Bucky Cox at the age of five, Jennifer Amyx at five, Mary Etta Boitano at five or six, the Garritson family (particularly Carrie), and Wesley Paul, a Korean-American who was a big star in South Korea by the age of ten. (I remember Desiree Ficker in road races when she was about five years old, although I don't know when she started running marathons.) Some of those kids were pretty fast. Back then, the attention was largely positive, though there were certainly rumblings about pushy parents and long-term health effects.
With a cut-off age of ten -- that is, eligible until the eleventh birthday -- I would expect to see some kids (both boys and girls) who could run close to 2:40, and it wouldn't shock me to see comparable times from the Olympic winners.