Earlier quoted context omitted.
Stick with PBS Kids and Sesame Street and Mister Rogers reruns.
If I remember correctly, babies learn to distinguish vowels from consonants from near birth when adults speak to them in that annoying high pitched "coochy coochy coo" dialect. After 6-12 months of life this starts to hold them back as they need to transition to hearing normal sounds and seeing the people mouthing them. The puppets with hinge-flap mouths, exaggerated and insanely high pitched accents in Sesame Street…
Elmo and several of the girl muppets are pretty shrill, but Oscar, Grover, Big Bird, and all the humans are normal. Kermit, Bert and Ernie have that rounded "muppet voice" which is kinda in between.
Screen time isn't great but Sesame Street is hands-down among the best childrens' television in existence.
Man, I kinda wanna watch Sesame Street now...