Parking sensors pushed in

[Supermike]

Our three year old toddler pushed in three of the rear parking sensors. While we were looking at the first two and wondering how they had disappeared, we saw her do the third one. Two questions:

- Is is normal that a toddler can push the sensors in so easily, or is this a defect? Shouldn't they be glued or otherwise fixed to the bumber?
- Since the repair is probably quite expensive in labour hours, can we do this ourselves? By the looks of it, maybe we just need to loosen the bottom cover plate to get to the sensors and push them back into their socket? Or is there more to it than that?

It's a 2013 Passat break (estate, station wagon, whatever you call it)

Thank you!