I read recently that in some languages, people are likely to call for their mothers in times of trouble.
The author (of whatever thing I read – I can’t recall what it was) said that this was very unlike what we Americans can sometimes shout in similar situations. I think it was her coy way of saying that we shout “motherfucker!” When others do the much softer, and perhaps more sensible, thing of just calling, “Mother!”
It is seemingly something we never stop doing, calling for our mothers.
Though, I’m pretty sure Polonius is not calling for his mother here. He does not yet realize it is he that is in danger – so he’s calling for anyone else.