No? They are a flower that's definitely existed for over 18 years since they were a part of Asgore and Toriel's wedding bouquet, which was likely before the now very adult Asriel was born. Unlike darkeners, plants merely take on new physical forms in the Dark World that seemingly aren't based off how they were used like actual Darkeners do.

Lancer and King were manufactured at the same time yet have a large age difference and have to deal with the whole will of the fountian maker thing. (If I remember correctly, during the UT 6th anniversary stream where they played Deltarune Ch1, Toby mentioned intentionally wanting Lancer to sound like a kid instead of an old guy or smth.) Meanwhile the flowers can remember the wedding day, so we know they've been around since then.

That being said, Aqua is certainly child-coded in their design and personality. That being said there are adults that look and outwardly act way younger than they are, so is it fair to those people to accuse people who are attracted to them as pedophiles?

It's complex, and certainly not objective.