In the current edition of the Little League’s Official Rules, Regulations, and Policies is a description and approved ruling for a runner’s lane violation.
Visit Rule 6.05(j) — The Batter — to learn how a batter is ruled out for running out of the baseline.
According to the Approved Ruling: In this situation, the lines marking the three-foot lane are a part of that lane and a batter-runner is required to have both feet within that three-foot lane or on the lines marking the lane.