It's tough to recommend an agency for nannies! The only time we used an agency (for a housekeeper, not a nanny) we discovered that she was not who she said she was, and was an unstable, possibly dangerous, person. The agency had done zero due dilligence. Most Peruvians use their networks of friends and family to find trustworthy people, so my recommendation to you is to exhaust all the possibilities of getting a personal recommendation first. Maybe somebody at your job can recommend, or a neighbor you trust..
Now, having said all that, I wanted to share something I learned about just last night. There is a website called workaway.info which provides kids from all over the world an opportunity to work in foreign countries in exchange for room and board (and overall good treatment). Sometimes they are also paid. They do all kinds of volunteer work, and basically just want a cheap way to live in a new country. Very cool.
Now, I noticed that there are people who post there for nannies too, so you might want to look into this, since you get the added advantage of having a nanny who can speak to your kid in English (or another language), if that is of interest to you. Anyway, I am just putting it out there. It might be worth a look into.