I'd have a quiet word with the actual teacher of the session and say that it's just a bit strange that this other instructor helps his daughter when none of you have the knowledge to help your children..
But, it might be that the other instructor is more senior than the children's instructor and that he/she can't do much about it. but no harm in asking.
[I am a jiu jitsu instructor btw. although not of children but if i was i would be happy for a parent to say this to me but if the other instructor was much more senior than me i might not be able to say anything as it's very heirarchical, depends on the dynamic, some instructors far senior to me i could say anything to, others i couldn't unless it was a serious safety thing]
Not sure if I'm bing pfb but dss (8 and 10) go for jiu jitsu. They really enjoy it but ds1 finds it hard because he is not at all aggressive or assertive. At the end of each session the class sits in a circle while children take it in turns to spar in pairs.
One of the teachers in the school (although he does not teach this particular session, teaches more advanced groups) has a daughter in this class and when it is her turn he advises her what to do throughout the sparring from the sidelines.
She is very physically strong and defeats her opponents. I don't think this is fair as the extra advice gives her encouragement and a technical advantage. None of the other parents cheer their children on in any way. I think we all pay the same and all children should be treated the same, or isthat naive?