Which used speakers in the 5K range?

Why do you feel that the Alto Utopias can't be around your kids? They weigh 167 lbs. each and would be very hard to tip. They are also tall enough that smaller kids wouldn't be able to reach the tweeters to poke dents in them (though that changes quickly enough).

Back when my first kid was born (1987) I bought a pair of speakers pretty well suited to toddlers and young kids: ADS L1090 columns. They were sealed enclosures, so there was no tempting port to stuff toys in, the midrange and tweeter were flexible domes, and the grills--difficult for little fingers to remove--were perforated metal, completely protecting the drivers behind. The columns had a narrow footprint, but I got the optional plinth bases to widen the stance, and these days you can get outriggers for nearly anything.

I'm not actually advocating for ADS speakers, though a pair of M12s or M15s might work for you. My point is that if you want speakers that are safe against little kids, they should be difficult to tip, not have ports visible and accessible, and the drivers need to be protected by something better than stretchy cloth.

You need to find something with hard-to-remove perforated metal grilles. That's what's great about many ADS loudspeakers including the M12s and M15s, but they're long out of production and it could get problematic if you do have to replace the tweeters.

I know there are current production speakers with perforated metal driver protectors, but don't know who they are offhand.

How about something from Martin Logan? IIRC the woofers are in sealed enclosures and the electrostatic panels are covered by perforated steel grills. Plus you can get some seriously high resolution high end sound from them.

Well, little kids might not be able to poke dents in the horn drivers, but they
could easily use them to store dolls and stuffed animals.

I just thought of another alternative. It's a bit of a paradigm shift from your
Alto Utopias, but you can get a brand new warranteed pair of Mirage OMD-
28s from Vanns.com for as little as $2600/pair. These were originally
$7500/pair and considered a bit of a bargain at that price.TAS reviewer
Chris Marten (seearch www.avguide.com) liked them so much he bought the
review pair and made them his reference. They easily reach down into the
20s, and they energize the room in a way that makes the entire listening area
usable.

When I went to Mirage bipolars in 1996, it was because with young kids I
could no longer sit in the sweet spot for any length of time; I was always up
and down for something. The Mirages maintained the same tonal balance
whether I was sitting down or getting one of the kids a snack or drink. I didn't
lose the soundstage when a dog walked in front of a speaker. The Mirage
grills over the mid/tweet assembly are perforated metal, held in place by
magnets, and they are very difficult for kids to remove. The speaker is ported,
but the port is not accessible to curious little hands--it fires downward into a
narrow space supported by a plinth.

These would give you a big very natural, room-filling sound, good
transparency with drivers made of light, stiff materials, and a very pleasant
presentation for not a lot of money. Even includes free shipping, a return
period, and the full factory warranty. I have had the OMD-28's little brother,
the OMD-15 for 4 years and like them *a lot*. Very easy to live with, yet
detailed enough to be able to draw you deep into the music.