Ulcer in Toddler's Mouth

Melissa • First Glow baby in December 2016, just found out I'm pregnant again and due in March 2019.

So, my daughter has been acting like something was bothering her mouth all day. I looked, expecting a piece of food stuck in her teeth, but instead, I see what looks like an ulcer/canker sore in the spot where her bottom lip attaches to her gum. She just turned two. It's obviously uncomfortable, but is there anything I can do to help it? Google search just says canker sore medicine and I don't think that apples for a baby.