Hi,
The babies are sometimes paler in color and can easily hide in your dense vegetation.. However, after 4 weeks or so, you should start to spot more of them here and there....IME, fish will eat things that fit in their mouths...while not personally familiar with the loach you have, it may in fact eat the little ones it encounters..esp if it is active at night, when the shrimp are not..
Try gently disturbing your plants and see if any come up....
I am no shrimp expert so cannot answer about their gestation period....and maturity rates...sorry.