Unfortunately, that's not enough. There's 3 criteria to determine if it is a harem.
1. Is there 3 or more reoccurring girls in the story? (Low chapter temporary characters don't count)
2. Are they all showing romantic desire for the MC?
3. (I forget this one sometimes) Are the girls the MC'S type?
In this case the answers are Yes, yes, NO.
The MC has made it clear that he has no interest in children. He refuses to marry the gnome girl because of that. That restriction also applies to the potion girl. Both these girls are disqualified.
The only girl left is the elf girl. Age 15 is typically the age a person is considered an adult in fantasy manga.
Harem only works if the possibility exists. A yes or maybe with work but Not a no.
There MUST be at least 3 ELIGIBLE FEMALE LOVE INTERESTS for a harem.
And thus, it's not a harem. The correct term for this is pseudo harem. It's not a harem. It just looks like one.

this need a harem tag