One of the things they really stressed in my safe environment training is to avoid even the appearance of impropriety, and that’s as much to protect the adult as it is to protect the child. It teaches the child what’s an appropriate way for an adult in authority to behave, but it also offers the adult an “out” in the case of a false accusation.
For example, we were taught that if a child needs to use a multi-stall restroom, escort the kid to the bathroom, and then stand with one foot in the door of the restroom and one foot in the hall. This will be visible on video cameras in the hall, so if, heaven forbid, the kid’s trying to set you up, it’ll be obvious you didn’t do anything, but also if there’s a predator in the bathroom, they’re not going to be pushing limits with a responsible adult right there.
Similarly, no single-out gifts. Another poster mentioned bookmarks for all, for example, and yep, that’s fine, or substituting a similarly-priced gift with everything being very obvious and above-board. If you gave all the other kids ribbon bookmarks and that one kid a $300 Pandora bracelet, that’s a serious problem both from the kid’s perspective (“Mr. Smith gave me this nice bracelet, so now I have to let him do things I otherwise might say no to,”) and from an innocent-but-unwise adult perspective (that kind of thing is NOT going to look good in either a legal court or the court of public opinion).