A 2-year-old boy died of heat exhaustion in Healdsburg on Thursday after his allegedly intoxicated mother left him and his 4-year-old brother in a locked van in 90-degree heat for about eight hours, police said. The mother of Liam Paulsen, 35-year-old Rena Corban, apparently began drinking in the morning and passed out on a couch when she returned home around 10 a.m. after running errands with the children, according to Healdsburg police Sgt. Toni Pinochi.