for f in *.txt; do wc -l "$f"; done

[number] [txt filename]
[number] [txt filename]
[number] [txt filename]

-main
    -folder1
        textfile1.txt
        textfile2.txt
        textfile3.txt
    -folder2
        textfile4.txt
        textfile5.txt
        textfile6.txt
    -folder3
        textfile7.txt
        textfile8.txt
        textfile9.txt
...and so forth