It's a subject I have been approached about before, and the older the kids get, the more it seems to come up. It's the creditors and predators argument if I can be so blunt. Creditors are easy enough to see, but predators can be far more elusive.
"If I give my daughter or son cash, assets etc, do I need to worry about protecting that against relationship fallout? (significant others)"
I personally believe that there are thresholds, either time or commitment related where much of this fear should wear off, however some things should be protected forever regardless. This link provides some insight into the treatment of gifts and inheritances as they relate to spouses and significant others of beneficiaries. I encourage you to read it, and if you have any questions, let's sit down and talk about it. It wouldn't be my first discussion on the matter, that's for sure.