It's not hard for me to give them names when I don't go for a theme.
My regular custom neighborhood has (or had, I've been marrying them off to playables and need to make more) scads of custom made townies that I didn't have much trouble with for names - the hardest thing was finding enough surnames to match some of the ethnicities.
The fantasy neighborhood had a gemstone theme for the Gen 1 kids, townie and playable alike, and I ran out very fast. For naming schemes that are that limited I'll keep it in families, where a name set of 20-30 names will last me 'til the neighborhood blows up.
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