You may wish to check out this link on Wikipedia about bats:http://en.wikipedia.org/wiki/Bat
These paragraphs in particular should be a concern:
"Their high mobility, broad distribution, and social behaviour (communal roosting and fission-fusion social structure) make bats favourable hosts and vectors of disease. Many species also appear to have a high tolerance for harbouring pathogens and often do not develop disease while infected."
"In the United States, bats typically constitute around a quarter of reported cases of rabies in wild animals. However, their bites account for the vast majority of cases of rabies in humans. Of the 36 cases of domestically-acquired rabies recorded in the country in 1995–2010, two were caused by dog bites and four patients were infected by receiving transplants from an organ donor who had previously died of rabies. All other cases were caused by bat bites."
"Due to the risk of rabies, and to health problems related to their faecal droppings in some regions, bats should be excluded from inhabited parts of houses. The Centers for Disease Control and Prevention (CDC) provide fullly detailed information on all aspects of bat management in North America, including how to capture a bat, what to do in case of exposure, and how to bat-proof a house humanely. In certain countries, such as the United Kingdom, it is illegal to handle bats without a license and advice should be sought from an expert organisation such as the Bat Conservation Trust if a trapped or injured bat is found."
Sure, bats are cute little critters, but disease-wise, they're basically mice with wings. I wouldn't think you would want them anywhere near your house. It might not be so bad if bats and mice would just clean up after themselves, but sadly that's not the case. They don't give it a second thought about where they create a mess.
On a more humorous note, allow me to recommend someone to help you get them out of the house.
Life! Life, do you hear me?! Give my creation LI-I-IFE!