Jennifer Haller will join Harcourt trade's children's division September 7 as v-p of sales, children's books. In the newly created post, Haller will direct the sales and distribution efforts of the children's group, including its marketing programs. The children's marketing group will report to Haller as will special markets for all matters involving children's sales. Haller, who most recently was national accounts manager at Houghton Mifflin, will be based in New York and report to Laurie Brown, senior v-p and executive director of sales and marketing.