Kid as young goat is from the 1200s with
Extended meaning of "child" first
recorded as slang 1590s, established
in informal usage by 1840s.
Dictionary.com defines kid as (informal) child.
You would use it in direct conversation with persons you know well
"Does your kid collect stamps?"
although I don't see it as too informal to ask someone, "Any kids?" instead of, "Any children?"
The OED dates boink as a verb back to 1984, citing Stephen King's Thinner, where it appears to be used as onomatopoeia, similar to bonk:
He half-expected them to begin bopping and boinking each other.
For this sense, the OED gives the definition "to strike, to knock", which is fairly similar to how bonk is used. As for the sexual meaning, their earliest cite is from two years later, a 1986 posting to the newsgroup net.singles by Andrew Tannenbaum:
When you and your honey boink away, you're doing what the doggies do.
Can boink be antedated? Perhaps. But take a look at the following chart from Google Books Ngrams Viewer:
So at the very least, boink wasn't widespread until after the mid-80s.
Searching Google Books, I was able to find some examples of boink from before 1986, but none with a sexual meaning. I chose to search for boinking first to reduce false positives because Google Books (unlike their Ngram Viewer) is case-insensitive and Boink is a name. I did also search for boink, but it was less useful. Searches for boinked and boinks had fewer false positives than boink did, but neither turned up any pre-1986 citations with a sexual meaning.
Most of what I found was like the following snippet from The Complaint Booth (Jack Kurtz, 1978):
Fairies pass through audience boinking people with their wands. Elves up and down aisles "beeping."
Here it seems similar to bonk. And we can find scattered earlier uses with the same meaning, as in the following 1966 use with a similar meaning in Science & Technology:
This causes a mechanical wave to travel around the circumference of the sleeve―in the same way it would if you kept "boinking" the top of a metal can with your fingers.
Using the same tools, Frank found an even earlier example, apparently quoting something Senator John Thye said in a 1947 congressional committee meeting:
Mr. Sears, how would you propose to perfect the general farm program, disregarding soil conservation which is just one small phase of the enter program, but boink back to parity price, the ever-normal granary, and those programs?
There are more like this, but it didn't seem to be especially common and none of the pre-1986 examples I found had a sexual meaning. Of course, that doesn't mean people didn't use it that way, only that I can't find it in print using online tools. It seems likely that the word was used in speech before it appeared in print, but I can only speculate as to how much earlier.
Given the dates, including the citation Frank found, it seems reasonable to guess that boink goes back about as far as bonk. As for the sexual use, it seems safe to say it became commonplace after the mid-80s.
Best Answer
The earliest dog named Rover I found is in a 1718 list of common names for hunting dogs.
Etymology
Rover was a common name for a hunting dog in 1718, along with other names such as Bouncer, Fiddler, Gallant, Lively, Ranger, Ruffler, Soundwell, Trouncer, Traveller and Wonder.
The name is most likely from rover, n.2 in the OED, specifically sense 2a:
This is etymologically from the -er suffix applied to rove v.2, the first definition in the OED being:
On the other hand, the etymology of piratical rover, n.1 (cf sea-rover) is:
1839
The boy's country-book (1839) by William Howitt features a happy dog called Rover:
1801
The school for children, or A selection of instruction and entertaining tales (1801) "from the French of" Vincent de Langres Lombard features a poem called "VERSES TO MY DOG, ROVER, WHEN GROWN OLD.":
And there's a song in The farmer's boy: a rural poem (1801) by Robert Bloomfield called "THE SHEPHERD AND HIS DOG ROVER":
Which was also printed in The Monthly mirror: reflecting men and manners (1801):
1780
A General Dictionary of the English Language (1780) by Thomas Sheridan may offer an etymology. The definition for ranger gives both "a rover" (presumably human) and "a dog that beats the ground" as synonyms for ranger. Perhaps ranger was first applied to "dogs that beat the ground".
1740
Poetical works (1740) by William Somerville (1675 – 1742) includes "The Officious Messenger, A Tale" which appears to feature a dog called Rover:
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1718
It appears in a list of "Hunters' TERMS, &c" in The compleat sportsman (1718) by Giles Jacob, and is given as a common name for a hunting hound: