My daughter doesn't want me to do anything to stop it. She thinks it's great. She even made me take screenshots to send to one of her friends.
The boy and his dad's lover have an option to "just be friends" and she says "whatever you do, don't push that!" She doesn't even want me to age him up to a teen.
It's not that abnormal actually. A lot of little kids develop crushes on teens and adults. The only creepy thing is that apparently the feeling is mutual. (They don't have options to flirt with each other though, just "romantic interest".)