As others have mentioned, it's under the friendly interaction. My sim children frequently gift pictures they draw and their parents have so far loved them!
My adult sim gifted a rose to his wife, and she was stoked about it. She was less enthusiastic about the tulip later. LOL I guess she's a rose lady! I haven't tried gifting flowers to parents from the kids. Maybe they have gift preferences as a hidden trait? It would be interesting to know if it's sim specific via traits, emotion based, or if it's just random luck whether they'll like it or not. His wife is romantic, so maybe that's why she liked the rose? You'd like she'd like the tulip too, then. lol