I'm going to go against the grain.
I've seen a lot of women wait until it's "really serious" before introducing the new man. It's an idealised sentiment borne of good intentions. It's also, IMO, rather naive.
What happens if you wait a year? By that time you're so invested in the relationship and put so much emphasis on the outcome of the introduction that the pressure itself can make the occasion horribly forced and be very counterproductive. And if things don't go well, with a 12-month history behind you - and let's face it you'll have been saying things like "if you get on well with the kids we can think about family days out/moving in, etc" - are you really going to be willing to call it off? Most probably, you'd be so heavily invested in the relationship that you'll make excuses and keep trying. And that's exactly how less-than-perfect family dynamics, including abusive ones at the extreme end of the scale, get established - because someone somewhere doesn't want to admit the unpalatable truth because they've invested too much to throw in the towel.
IMO the right time is quite soon after you've established it's a committed relationship that you hope will go somewhere. That varies depending on how often you see each other and how open you are with each other. The trick is to keep it light and not to encourage bonding.
Children meet new people and move on from them all the time with no lasting damage. Think of teachers, for example. A boyfriend is no different, provided you don't let him bod too closely. Don't let him put the DC to bed, get too cosy reading stories/playing with them/tending grazed knees, etc. Let him be as involved as a friend who maybe isn't a parent and has no interest in being one but good-naturedly tolerates your DC without actively engaging them. And don't do it too often so that family time is still viewed by your DC as meaning you and them exclusively. There should be a clear distinction that your BF is outside the inner family circle. Keep it light and infrequent.
If the relationship falls through, or if your BF reacts towards your DC (or they to him) in a way you find incompatible so that you call things off, you might be met with questions from your DC about XBF's whereabouts but there will no emotional fallout, just as there wouldn't be if a friend moves away.
If, after time, things are still going well, you then work on the level of bonding and the frequency of it.
One thing I do agree on though is don't pretend your BF is just a friend. DC will see straight through it and could possibly distrust you (and maybe BF) if they believe you are being less than honest. And why would you? I want my DC to know that they should "try out" people before deciding to commit the rest of their lives to them. You're simply modelling that.
Good luck.