Do you really need source for when toys are selling best!? :D
Labo is quite different than any other product on gaming market (Wii and Kinect were not aimed only to kids/parents market), and no, not every popular Nintendo game was selling great from start.
I think it's gonna sell like like a normal game meaning its sales are gonna be front loaded then taper off. If you want to compare it to toys, sales likely won't pick up either because toys are very hit or miss. Labo has been out long enough that if there's no labo craze yet, it's not gonna happen.