Let us assume you have some young children. Now on occasion you may decide that you don't want your young offspring to tag along somewhere and leave them in the care of someone else. It happens. It's acceptable. It's better than leaving them alone in your room while you and your friends go to the restaurant across the road for a drink that's for sure. Anyway, logically you probably want to leave your kids with someone you trust, but frankly that can be hard work and actually cost you money! So now, you can leave them with anyone you like and just ask the police if they're a wrong un. Yes, now you don't need to worry about having a society where you might trust another person, get 'em all checked out!
GAH!
Put simply, if you don't trust me when I say that I haven't actually committed a variety of sex crimes and managed to hide the convictions from you then you obviously don't trust me enough to be anywhere near either you or your children. If you honestly think the risk of me being around is high enough to merit a police check then I don't think I want to be around you. This isn't just random concern about leaving your flesh and blood with someone else, it's paranoia and if you doubt me that much neither of us will ever be happy with our relationship ever again.
On the first of many, many levels that this is completely screwed up; family can ask for checks. Family! I think my sister would've noticed had I been convicted of any crime. I think my cousin would've noticed and they live at the other end of the country!
How about this wonderful phrase "potential boyfriends"? Well I'm male so logically that make me a potential boyfriend for anyone interested in men, plus anyone who thinks that maybe one day they could consider it. It may be unlikely, but potentially it could happen. So even if purely for logistical purposes we assume you need to wait a month before getting your latest suitor checked out, again I'll come back to the idea that if you have enough of a doubt that you want to check you obviously don't trust them anyway! What kind of relationship do you have if you feel the need to ask the police if the person you're smitten with and have let into your life is hiding something of this scale from you?
This really isn't the same scale as standard checks for people who work with children; in those cases you have no relationship at all and are trusting the system not the person. In that case police checks are valid and sensible. Not foolproof, not even really much protection in fact, but a quick, handy, early warning filter. This is about a complete destruction of trust within society. It's a knee jerk reaction to keep the bogey man at bay and like so many of these coddling laws it erodes the very foundations that should work for our society and makes the world a slightly more dangerous place.
If you're honestly worried about your kids then hire a professional – they will not only have been checked, but their premises will have been checked, they'll have insurance for all kinds of nasty things, they have had fire safety checks, possibly first aid training too. If you want your friends or family to care for your children then simply trust them, if you don't then why on earth are you handing something so precious over to them in the first place?