Can a long dress simply be shortened?

Yes

Yes you can, that is what my BMs are doing after my wedding so they will get more use out of their dresses. I don't think it will be a huge issue for kids because it would be hard to make a dress look perfect.

I understand what you're asking so it would depend on how the dress flows. If it goes straight down it should be fine. EIther way it should be fine, just contact a seamstress to get a professional opinion.

I had a vintage satin wedding gown with a train shortened to tea length. It was more of a ballgown shape, but looked great short with a crinoline.

If your dresses have layers, it will cost more to hem.

I'm sure you can have it shortened no problem, but of course there will be a cost. If its pretty plain on the bottom (chiffon or satin - not lace) it shouldn't be too expensive.

I did that to my wedding dress... lol

Definitely possible. My Co worker just did exactly what you are requesting to two prom dresses today. A little different than BMs dresses but still an alteration. It was simple. She had the wear the dress and cut of the unwanted material and then hem the bottom.

Yes absolutely - if its A line and simple it's super easy for a seamstress to do

Are you sure the designer doesn't offer the shorter version? My bridesmaids dresses had the option of tea length, knee length, and long.