Xargs pass input to command that contains a pipe
Here you are with xargs:
find . -type d|xargs -I % sh -c 'find % -type f -maxdepth 1 | head -1'
But remember: internal loop is much faster!
time find $PWD -type d | while read dir;do find $dir -type f -maxdepth 1 | head -1;done >/dev/null
0m09.62s real 0m01.67s user 0m02.36s system
time find . -type d|xargs -I % sh -c 'find % -type f -maxdepth 1 | head -1' >/dev/null
0m12.85s real 0m01.84s user 0m02.86s system