Ive answered this here and edited the below with some new research and things I've learned since: www.reddit.com/r/AskHistorians/comments/2r4sq7/how_did_couples_with_children_have_sex_in_one/cnch359

They just had sex. Couples would have sex with their children or relatives in the bed, there wasn't the sense of taboo or privacy around it that we have today.

The term you are looking for is called "the invention of privacy."

The works and research in this field is somewhat obscure and highly complicated. The most important book, La Vie du privee--The History of Private Life--is nearly four volumes long. The other major (recent) work by McKeon is about 1000 pages and very difficult to read as a layman (or even as an expert...) and is called The Secret History of Domesticity. Additionally, you have to take a deep dive into church court records such as Ingram and Addy.

Prior to the sixteenth century in most of Europe, and well into the seventeenth century, there less of a reaction to what we would call semipublic sex, nudity or sexual organs. These things were common, from what we know of surviving records in London, Paris, Florence, Venice, Milan, and other city records. For example, there were Cock and Hen bars in London, which would be equivalent to a singles bar today. In these clubs, what we would call nonpenatrative sex was on more or less public display, and indeed, it was common to see it in the streets as well.

For example Addy writes in Sex and Sin:

Drunkenness could also lead to adultery in the alehouse, as happened at Clayton-le-Moors where Henry Byare saw Mary Darwin commit adultery. Her husband was sleeping off his drunken stupor on the alehouse floor, and Mary went to another room where Henry saw her with a man on a bed from which he heard ‘much puffing and blowing’. Some women took offence when reports circulated that they were seen drunk.

Part of the reason for that is because there was no police force to enforce public decorum as we have today. And even if they were, they would not necessarily have had the authority to do anything about public lewdness, drunkenness, or other misbehavior as we would see it. In fact, it took nearly a half-century after the establishment of the Metropolitan Police in London for them to feel as if they had sufficient authority to punish morality offenders (see the numerous King and Queen declarations on this, esp. Victoria's relation with the Police).

The larger part of it, however, had to do with 'the invention of privacy.' What I mean by that is that in the late middle ages and early renaissance, it was quite common for households to be one room, and in particular, to have one shared bed for the entire family. This meant that children would be in bed and in all probability witness or be aware of their parents making their siblings. Additionally the vast majority of the public lived in the countryside with animals and would see animal copulation at one point or another in their lives. Here's Ian Moulton:

[Over the course of the seventeenth century] Bedchambers-and the beds themselves-slowly shifted from being common living areas (in lower-class homes) or sites for social gatherings (in upper-class ones) to being what they are today-private space for the single person or couple who sleep in them. Reading became dominantly private and silent rather than spoken and communal.

One of the major reasons for the shift is that building material became much cheaper and architectural knowledge became much more common, allowing the creation of multiple rooms, better heating, and what is termed 'the creation of the upstairs.'

Additionally, there was just a greater concern with the protection of a person's name. Addy and Ingram see a sharp increase in the number of church court cases until the end of the 17th century until their dissolution. The public behavior became inappropriate and the state began to enforce laws against it with increasing severity.

Of course, this is not to say that no one hid intercourse or tried to achieve privacy before this time period, but it was much different than it was today.