First (I read the questions you posed on the profile), there is a template for a child who died young:
{{Died Young}} Just place that under the == Biography == header.
== Biography ==
{{Died Young}}
Second, you can discuss the Geneanet tree, but you are correct in that it is not a source, just like and Ancestry tree or FamilySearch's IGI is not a source. Under the == Sources == heading you can put a See also: section:
== Sources ==
<references />
See also:
* Geneanet Family Tree. Put a link to the page so other people can have a look.