Creating a site that shows different content to children and adults – help

Hi I am looking for some advice…
I am creating a site for a primary (ages 4-11) school teacher that wants to display homework games, activities and videos for children.

However the site is also planned to have further information for adults, including information on the child activities for parents, lesson plans and activities for other teachers.
Ideally when a visitor comes to the site they will say if they are an adult or child and show the correct content throughout the session.

For children, no adverts will be displayed, and menus will be more graphical. Obviously children under 11 should not have social media accounts or email addresses, so registering is not an option for them and would not appeal to making a child friendly education site.

For adults more information will be available on each post, some adverts displayed, links to other sites and social media sharing options. The greater content will require more text based menus.

I’m struggling to work out how to do this, I’m quite a fan of Atahualpa, and considered using widgets for menus, making adults register for the site and only showing the “adult” info to logged in users, but that would mean if a parent/carer logged onto the site and didn’t log off then let their child use the site they would not see the child-friendly version.

Any ideas on ways forward? Is creating 2 separate sites the best way? What will that mean to SEO though?

All suggestions greatly appreciated!
All the best, and thanks in advance.