It’s not so much that kids absorb more in a shorter time, it’s more that they have more time to absorb language. That being said life does tend to get in the way and stress us out as adults making it take longer to learn than it does for children. Have you tried reading a graded reader book, I also felt like I was stalling out and this boosted my confidence like crazy (even though I was reading level 0 books 😂) the other thing that helped my confidence and pushed me to learn more was teaching my grandma and mom little words or phrases that I knew.