What happens to couples and sex when children are born

There are those who talk about it and those who do not, there are those more and there are those less, but when you go from two to three, that is, when you turn from a couple into a family, sex suffers. And a lot. According to more or less official statistics but plausible according to sexologists, for 90% of new parents with the arrival of a child, sexual activity fades, dilutes, for some it even disappears.