Column chart with Joined Tables

Anonymous  You can do this in Power BI with a merge in Power Query or with relationships. Power Query merge lets you do a join on two columns (UserID and CreatedDate) as you have done in your SQL query. 

Relationships can only be done on 1 column, so you'll need to create a new merged column (this can be done also in Power Query) in both the Children and the User table: Open the Children table in Power Query, select User column, hold Ctrl, Select CreatedDate column, in Add Column tab click Merge. Choose a unique separator (|, or whatever works for you). Repeat this same process in the User table.

Now you can create relationships in Power BI on Merged > Merged and UserID to ID. 

Then create a new measure: 

Age = AVERAGEX(Children, DATEDIFF(Children[CreatedDate], Children[DueDate], Week))

Then put in a visual with User[CommunityEntryId]