This should be official but it’s done by another artist. This one is well done!
The mangaka has her own retirement plan now. Just make new releases of “Bloom Into You” when they’re older! (No, really, she’s got a gold mine here with this intellectual property)
But they already adopted two kids, plus Tsuruno basically lives there anyway and she is so energetic and bouncy on a good day that it's like having a third kid, despite her being older than Iroha.