"Adult" ads on YGroups that may include children: How can we block ads of this type?

[Garummm]

Our Yahoo Group is private because we anticipate that we will have youth joining us in the future, and because a Yahoo Group is so much more secure than Facebook or other options.

We also recognize that advertising is a necessary feature. Is there any way to de-select "adult" ads? We've been getting more of them lately: "dating" services with semi-nude females, and such like.
Our YGroup is NOT categorized as "adult".

This is embarrassing, after we explain that we use Yahoo because is is a safer option than Facebook for children and youth.

I remember (not sure if it was in Yahoo) that I could select specific categories of ads that I wanted to receive (makes the advertisements more effective, too). There was a certain minimum number of ad categories that I had to select -- with enough margin to allow me to not choose "adult" ads and the like.

This seems to me to be an optimum system: the provider still generates ad revenue, the advertiser gets a more interested audience, and the user can opt out of certain categories.