White tissue growth in the mouth of my toddler

Hello
I would be really grateful if you share thoughts or ideas about this situation...
My boy is almost 18 months old and he has 6 teeth so far, but just today I noticed him doing "lalalalala" sound, like something was causing him to do it, and I checked inside of his mouth and saw, a very soft, short strip of what seems to be white flash growing or coming out of his gum where I can also see a tooth under the skin..Any idea what can this be?
Thank you