A lot of young peoples found the Au Pair program very difficult and they couldn't integrate.
A very important reason is the lack of communication between Au Pair and Host Family.
The communication is the key for a good start. Talk to you Au Pair on the phone before arriving to make sure you do understand each other. After they join you family let them know their duties and the house rules. Write them all down and go through them together. If any problem appears on the way do talk about it and try to resolve it in a polite way. It needs time to know each other and adapt. Try to get to know each other's culture as this is a important matter for understanding. Make the Au Pair feel part of you family. Take them with you on holiday if possible and enjoy some time together special with your kids. Stick to the rules and be fair and clear about them.
Always TALK if something is not clear!