Nintendo Labo came in at #4 overall for April 2018 sales in the United States. NPD doesn't provide sales numbers along with their charts, but NPD analyst Mat Piscatella did give a little more insight into Labo's debut.
“Solid debut month sales —certainly not fantastic and definitely not terrible. The story for Labo will really be told in the months leading to Q4 and, of course, in holiday. I think the April sales set a solid foundation, and I don’t think anything in the April data suggests anything more than that. The market jury is certainly still out. It continues to be something very difficult to analyze and predict, certainly.”