The ability to schedule child/story-level issues with dates is available for Kanban projects on Jira Software Cloud on all editions, Free included.
More here: https://community.atlassian.com/t5/Jira-Software-articles/What-s-new-in-the-Roadmap-view-I-m-so-glad-you-asked/ba-p/2077594
For scrum teams, child issues are scheduled according to the sprint to which they’re assigned which follows the scrum framework of delivery. On your roadmap, the schedule bar for all child issues is the same size regardless of their estimated duration, aligning with the sprints at the top header of the roadmap. https://support.atlassian.com/jira-software-cloud/docs/schedule-work-for-scrum-teams-on-your-roadmap/
On Scrum projects/teams - When all story-level issues are visualized with the same duration, it is difficult to visualize dependencies between issues within the sprint. It becomes a little harder to sequence work, depending on how long our sprint cadence is.
It would be great to improve the ability to plan & sequence work within a sprint, which could be through a different visualization or by utilizing the start/due dates on each issue to show the timeline bar accordingly.