Yes you can ask for child related tasks to be done. You could also ask for household related tasks, some nannies may object, while others will be fine with that.
Personally I don't Iron - I'm no good at ironing (like a lot of men I expect).
On Friday I did 3 loads of washing, only hung 2 loads to dry (other load was finishing as I left work). Mixed loads of adult and child clothing... sometimes I find it easier just to do lights / darks, rather than just child lights, child darks etc.
General vaccuming, tidying of communal areas and children's bedrooms is fine.
However, if the nanny is doing housework, the children are not getting a great deal of attention - fine if one is asleep, others at school/pre-school.
As you are interviewing next week, add a question to your list... asking prospective nannies what household duties they would expect to be doing, if the children were asleep / at pre-school. Keep it an OPEN question, so they can talk about what they have done in the past, what they would expect to do. Don't ask CLOSED questions such as "Will you do Ironing", as this results in Yes/No answers - makes interviewing hard for you, if you do all the talking and the prospective nanny just says Yes/No to each question.