WBS is in the Scope Baseline (refer to PMBOK page 161). Scope Baseline is the approved version of the scope statement, WBS and the WBS dictionary. Scope Baseline is an input to Define Activities.
A project charter has the summary milestone schedule (refer toPMBOK page 81) which is used as an input to Plan Schedule Management process. Schedule Management Plan is one component of the Project Management Plan which is an input to Define Activities.