Hellobee Boards

My DD also does this (not to the point of skin irritation though). She's 3.5, and we've gently discussed it a bit - like that she gets the bump on her thumb from doing it, and how she gets germs in her mouth that way....talking (not shaming, just mentioning why it's not a great thing to do) seems to have made her aware that she does it and reduced it a bit. The other day she was upset and told me she wanted to suck her thumb. I told her of course she could but asked her what might be a better idea to make her feel nice if she was, say, at school. She thought of rubbing her stuffed dog and sitting on my lap as two alternatives that made her feel good.

For a younger child you could just say "I see you're sucking your thumb; do you want to have a rest/smuggle/etc.?"