One approach is to clean it up for your performances. Then provide a the teacher with suggestions of supplemental exercises for the kids to complete after you have left. This could include a reference to an original source.

I think the kids are unlikely to remember that you switched a word or two years down the road. The important thing is that they have the experience in the first place. This won't happen if you are considered too controversial and are not hired for future gigs.

I think your role in that age group is to keep them curious, expose them to new ideas and experiences. Years later, they can figure out what the correct word should have been.

I have been teaching "This Land is Your Land" to my young grand-children, but I am careful to omit the later verses because the parents may object. The kids won't remember which verses I sang when they were preschoolers.

I am so glad that children have this opportunity. In my school, singing was limited. History was remembering dates and places of battles and politics. I hated it.