Baby's upper lip connected to gums?
That connector is called a labial frenulum. In some children,
the frenulum is elongated and attached all the way down their gums
between their two front teeth. This can cause some problems, such
as an inability to breastfeed, speech delays, or gapping of the
front teeth. This can be corrected, if necessary, by a doctor
cutting it in a procedure called a frenectomy.