Hi stressed, I don't think it is usual to sign a contract with an aupair, though I can see it is good practice. My new aupair who is starting in September specifically asked to sign one, so I drafted one up. But I would not otherwise bring up the issue of a contract. I believe most families just rely on a set of house rules and timetable which are communicated to the aupair ahead of or more usually on arrival.
25 hours + 2 nights babysitting is referred to as the norm, but you can agree any set of hours or scope of work (within reason) with your aupair. I find that more often than not, families seem to require aupairs for more than 25 hours, so your 35 sounds fine, provided you pay more pocket money.
The important thing is to make it clear to the aupair what you require before you make the offer, highlighting any potential snags. For example, in my case, my aupair has to do my dd's school run on foot which involves 25 minutes of walking each way and she has to change my ds' nappies. I make that clear in advance.
I quickly looked up the European Agreement in the past - this is what I learnt ie DON"T incorporate it into your contract as it does not apply to the UK (cutting-and-pasting from a previous thread):
The "[Council of Europe's European Agreement on Au Pair Placement 1969] was only ratified by 5 states, UK not included.
Read more from this page from the European Committee for Social Cohesion :
"3. At the outset, the CDCS would like to stress that the employment of an au pair is intended primarily to promote cultural exchange between young people and very rarely leads to situations of domestic slavery, despite the occasional cases of abuse that have been reported.
The European Agreement on Au Pair Placement dates from 1969. It contains provisions ? now obsolete ? on the relations between the host family and the au pair. In view of the small number of ratifications (five member states), the CDCS began by considering whether it would be worth revising and updating the Agreement. The replies to the questionnaires it sent to all the members showed that this question excited little political interest and that very few states would ratify the Agreement even if it were altered.""
If you are looking for a standard aupair contract, I found this one to be closet to the spirit of an aupair arrangement: here. I also put in a sentence about the aupair having to comply with my reasonable houserules.