The OED defines this noun as: “A person who has charge of or looks after a specified thing or operation, esp. in the course of employment. Without defining word esp.: = baby-minder.” There are many variants, in the realms of public relations, crime and sport, where it refers to a goalkeeper.
Indeed, one indication that minder has moved to NOOB status is this recent quote from a New York Times blog about (U.S.) college hockey: “Patterson had 44 saves on the weekend, Tigers’ net minder Josh Thorimbert had 73.”
There was also this from the Times capsule review of “Alvin and the Chipmunks: Chipwrecked”: “The furry guys and the Chipettes, the gal pals they acquired in an earlier installment of the franchise, find themselves shipwrecked along with their human minder, Dave (Jason Lee).”
In a similar human-on-animal way, there is a dog-walking company in Philadelphia called Monster Minders.
If further proof is needed, I offer the fact that minder recently figured in the popular TV series “Gossip Girl.” I confess I couldn’t udnerstand the references I found on the web, so I turned to my colleague Dawn Fallik, a “GG” aficionado, for explanation. She did not disappoint:
Blair was married to King Louis. She never really loved him, so she came back to New York while he headed to Monaco. But he send a royal minder to watch over her every move, so that he’d find out if Blair cheated on him, thereby annulling the marriage and costing Blair big money in dowry. Alas, it turns out the minder was secretly in love with the prince and did all she could to help Blair slut around. The minder is now back in Monaco.
notoneoffbritishisms.com 
Good little boys and girls have been *minders* of their Ps and Qs at least since the Jazz Age, and printer’s devils doubtless since before that. There are several theories as to the origin of this usage, one being that the letters originally stood for pints and quarts in British pubs and taverns of the 17th century. The phrase, “mind your Ps and Qs” doesn’t seem to appear much in English literature, however (per Google’s Ngram Viewer).
“Minders” has entered American politics with “handlers” to mean
those who guide the novice candidate.
You’re saying “minder” in the sernse “goalkeeper” is a Briticism? I’ve always assumed it to be an Americanism …
Maybe the George Cole & Dennis Waterman tv series “Minder” never made it to your side of the pond. Wouldn’t surprise me: quite a bit of Cockneyspeak. The “minder” in question was a bodyguard – this being the term used in the demi-monde at the time.
Can I just chip in that ‘mind your ps and qs has nothing to do with pints and quarts – it is a printers’ phrase along with ‘coining a phrase’, ‘come a cropper’, ‘cliche’, ‘upper case’, ‘lower case’.
As a Brit have never heard minder used for a goalkeeper – ‘goalie’ is more or less universal.
Childminder is now used extensively but babysitter was more common when I was growing up in the sixties and seventies,
Minder as bodyguard or escort comes I think primarily from the 80s TV series of that name but may well have been actual cockney slang before that.
Incidentally I heard it used a couple days ago by a young lady who is a full-time political organiser and had to serve as minder to a 16-year old party member who made a speech at last year’s Labour Party conference and was mobbed by the press for days afterwards.
In the US you’d presumably have to use something like publicist or PR or flack or spin doctor for that role none of which sound right to me.
1. This claims that “come a cropper” has nothing to do with printing: https://www.phrases.org.uk/meanings/come-a-cropper.html
2. The folk etymology for minding one’s Ps and Qs is that it is an injunction to remember to say Please and Thank you (“Than Q”.