Outings With Family Members

My husbands aunt mentioned that she wanted to take our son out to do something for his birthday instead of getting him a gift. She used to be the 'fun aunt' with my husband's generation and took them to theme parks and outings often. Our son is turning 3.

I am hesitant, but my husband told me 'we have to let him start doing things with people who aren't us some time'. Most of his family parents VERY differently than we do. We don't raise our voice, we don't use corporal punishment, and we use love and logic discipline. We also allow our son to negotiate and do things independently, and we allow him 'dangerous play' as well. I'm hesitant because his entire family (almost) pretty much do the opposite, so I worry that he'll want to do something and expect loose supervision and she'll want him to hold her hand the whole time and it'll result in a meltdown and she won't know how to handle it.

At what age would you or did you allow family members to take your children on outings of some kind?