Here's another graph using the DENOM16 variable from the General Social Survey. That question asked respondents which religious tradition they were raised in, and by calculating their age, we can generate an estimate of the religious affiliation of 16-year-olds since 1910. (For more details).
As you can see, several of the Mainline Protestant denominations have dropped steadily over the last 100 years. At the start of last century, a full 20% of American youth were raised as Methodists. Now it's about 3%. Protestants and Presbyterians have likewise dropped. Episcopalians, in contrast, have dropped a bit, but there weren't that many to begin with.
Baptists, however, have kept their numbers at 19% to 24% the whole time, though they have lost some of the gains they made in the mid 20th century.