Mariano Romero Reynaud shot a 71 over Gullane No.2 to take a one-shot lead in the 15-18's section over his compatriot Jose Manuel Romero.
Playing over the same course, Hendrika Labsch, a young German, shot a 73 to lead the girls' 15-18 age group.
Scoring was even more impressive in the boys' under-14s and under-13s events, which are also being played on Gullane No.2. Playing in the under-14s event, Simon Zack of the Czech Republic shot a 68, as did UK duo Fraser Davren and Robert Macintyre in the under-13s section.
On Gullane No.3, three under-14 girls – Rebecca McGeechan (Germany), Harriet Wilson (UK) and Celia Mansour (France) – had 75s, as did another German competitor, Jana Wuensch, in the under-13s.
Eloise Healey and fellow UK challenger Ella Ofstedahl had 70s over the same course in the under-12s on the same course, while the UK's Lucy Walton and Monet Flores from Guatemala had 68 and 73 in the under-10s and under-11s respectively.
Two Americans lead the boys' events. Ryan Goldfarb from New York hit 76 over on Gullane No.3 in the under-9s, while Dylan Fritz from Las Vegas shot a 35 over nine holes at Longniddry to share top spot in the under-8s with Carlos Phillipe Winsett-Palanca from the Phillipines.
Also at Longniddry, George Leigh (UK) and Wolfgang Glawe of Germany had 32s in the boys' 7 and unders, while Slovenia's Lara Jecnik (8 and unders) shot 33 and South African Wong-ju Son (under-9s) a 34 over nine holes in the girls' events.
Craigielaw staged the remaining three boys' events, with the pacesetters being Czech Republic youngster Matyas Zapletal (72 in the under-10s), the UK's Marco Penge (70 in the under-11s) and compatriot Maxwell Martin (69 in under-12s).