There was an experiment by a linguist who wanted to see what would happen if he spoke only Klingon with his son. https://youtu.be/7BRInEvS0e4

It doesn't seem to have reached any conclusions: positive or negative. I suspect that the same or similar may have happened if it had been Esperanto, because the child's mother continued speaking English and presumably everyone else, including the one-way chatter of the TV.

I still maintain that Klingon is just a plaything, but it's interesting to find out if (like other languages which are more complicated) it can be acquired in the same way 'natural' languages are.