Question about Aptoide
After some research this is what I came up with.

Did you download an APK for some app from the Aptoide website recently? If so, you didn't download that app. You downloaded the Aptoide market, and that market downloaded your app. It is likely that one of the kids tried to free download a paid app, as I see there are a lot of them in Aptoide. :) As always those free market apps are not trustworthy at best (they may look clean enough but they might still be sending sensitive data to their servers), and malicious and virus-infected at worst. 

Here is a list of what I came up with each of the apps you mentioned:


"Messagerie Double" means "Double Messaging". I didn't find anything specially useful about this app, but based on what I've seen it looks like the Samsung Dual Messaging function, hence a system app.
"SEMFactoryApp" should be a system app, as it was mentioned in this Reddit Thread. Also, this JoeSandbox analysis dodn't detect any suspicious code in this app, so it looks like it's safe to assume that it is a system app.
"SVC Agent" looks like it matches com.samsung.android.svcagent, which is in this debloat list on XDA, and this thread on Android Authority also mentions that, so it looks like a system app too.
"NetworkDiagnostic" is mentioned on this APKMirror page as having package name com.samsung.android.networkdiagnostic and it is also in the debloat list above, so likely a system app.
"slocation" looks like a system app too, considering it didn't go away after a system reset as mentioned here.
Finally "bootagent" also looks like a system app, refer to post #147 here.


So why does Aptoide display system apps? Because it doesn't distinguish between system and non-system apps, and someone named sirkesyone-applikes (clearly without a proper knowledge of system apps) uploaded those system apps to Aptoide. If you or one of the kids mistakenly hit "Update" and confirm the update on one of those apps it could update to a wrong or incompatible version and brick your phone or erase your data or etc. So I would recommend uninstalling Aptoide as quickly as possible. :)

Good Luck!