Answer. I'm confused. May I assume the grandmother or her sister are at least 55 years old? If so, they qualify both as to the requirement that there be at least one occupant 55+, and as to the second person requirement. That should be the end of the age issue.
As for the babysitting, this is not a for-profit enterprise, so presumably does not violate any rules you might have for such situations. So all it is is family visiting, which is permissible under the rules. So long as the children are not staying overnight, I do not understand there to be a 30-day limit on this. If they do stay overnight, it appears there is a 30-day cap. But you don't say whether the 30-days is consecutive or cumulative. Unless there is some reason to believe the grandmother is lying about the children staying overnight (and even then, there is the 30-day rule) I don't see anything that suggests a violation. I know of nothing under the 55+ housing law that places restrictions on family visitors under age 55. In fact, as you may know, 55+ parks are permitted to have up to 20% of their spaces rented to families (which is not something should consider for a variety of reasons). However, the point is that the presence of children in a 55+ park does not, per se' cause the park to lose its 55+ designation.
I believe this situation demands a practical approach. Is the babysitting situation causing a problem, e.g. noise, disruption, children in street, lack of supervision, etc? Are other residents complaining? If none of these consequences are occurring, I don't see a concern, or a need to start counting days, etc. If the situation is not being abused, I'd leave it alone. You may want to privately discuss this with the grandmother, just to make sure she understands that it is important that she monitor her grandchildrens' activity at all times, just to make sure other (less child-friendly) residents don't complain.
The take-away here is that while rules are important, so long as they are not being abused, the need to be concerned primarily arises when there are complaints from other residents. If no one is complaining and the rules are not being blatantly abused, it does not seem necessary to become concerned.