how old are they ?
they might get asked to attend an interview depending on their age, but i doubt it.

UKBA might state that your wife's friend has sole responsibility of them and not your wife, so explain to her friend, its possible she will get a call from the ECO, if they they do call her, she needs to explain that the children were only left with her temporary and she never had sole responsibility.

info is here ..
http://www.ukba.homeoffice.gov.uk/vi...applying-visa/