OK, here goes.
Curing fish is an almost necessary thing to do for sashimi. It is related to 2 things...taste and texture. The cure firms it up, and obviously season the fish so it tastes better.
The curing process could include things like sake or mirin. Similar to using pernod, brandy or aquavit when curing gravlox.
The liquid part is not necessary though, it is only for flavor. So you can easily leave this off the fish with little not no ill effect.
I don't really think that alcohol allergies are common enough to effect the general public. I don't think I've run into it very often in my career. Most people with a true allergy to something will let you know, and you can always use it on some dishes and leave it off a couple in order to keep an option or two for allergies. Like, you could use it for salmon and mackerel, but not for the scallop (or whatever).
I wouldn't worry about kids. Not too many kids eat sushi, and even if they did, the minuscule amount of alcohol on the fish isn't going to affect them in any way. That is a total non issue to me.
But I highly recommend curing your fish. Most really good sushi places do it. Just to be clear, we are not talking about the type of cure you would use for a smoked fish, or a cured fish like gravlox, these are lighter cures meant to firm up and season the fish. The firmness makes cutting the fish much easier and more consistent, improves the texture for eating, and makes it taste better. No brainer.