I copy a paragraph from a word doc into Writer OR I copy a cell from excel into Calc.
When I paste, the [unwanted] parent formatting is pasted as well -
can the child document be set so that this is avoided without the need to paste special every time?
In calc unformatted past is on the right arrow of paste bottom.
Or on Shift+Ctrl+V
I already use Shift+Ctrl+V. Although a useful comment, Q was really whether the child document could be set [default formatted] to receive pasted data unformatted - looks like the answer is no.
The preferred solution seems to be from [Solved] Default Paste (View topic) • Apache OpenOffice Community Forum
Tools → Customize. On the Keyboard tab choose the category Edit and scroll through the Function list to Past Unformatted Text.
However, I no longer see this function in the list (tested LO 5.4.3.2 and AOO 4.1.3).
So instead, use the macro at Paste unformatted text default option.
Thanks: I count this as ‘answered’ for me because I’m operating on 14.04 and Synaptic tells me that LO 1:4.2.8-0ubuntu5.3 is the ‘Latest Version’ and so ‘Paste Unformatted Text’ shows as a valid option in the Function List, but I hit a snag on this as ‘Paste Unformatted Text’ ONLY shows as a valid option in the Function List IN WRITER - very strangely it is absent as an option in CALC.
Although not a direct answer to the Q, for my purposes, Ctrl+Alt+Shift+V from Jim K’s links is also a solution [but only in Writer].
However I appreciate that this question may not be ‘answered’ for users of 5.4.3.2 etc
Should be not so easy find people answering question here using 4.2 version LibreOffice Release Plan
@nic: Good additional information. To close out the question, please click the 
next to an answer. See guidelines for asking.
Can’t tick my own answer - not enough points.
m.a.riosv: thanks for the useful link. Q [not for this forum!] is why Synaptic in 14.04 says LO 1:4.2.8-0ubuntu5.3 is the ‘Latest Version’. I am very reluctant to take anything until Ubuntu has cleared it and put in Synaptic after having lost many days of work to a bug in Calc a few years ago. Perhaps LTS on 14.04 doesn’t extend to versions of LO?