Carly Stinson is the mother

[Andrew Simone]

Barney's half sister Carly is Ted's wife. boom.

[Danno]

heheheheheh

[Tardis Tasha]

This has long since been my theory. 

But the writers are tricky bastards. :)

[Zach]

I am still hoping for the kids to be adopted and the whole purpose was to tell the kids the legendary adventures of Barney Stinson. boom.

[Danno]

but... they've met...