To be fair, I presumed the same as Mokole & Tawmis (though not the Emma Frost part) as the whole "Legacies" programme going on through Vol.2 suggested that the Hull House kids were all 'children' of existing heroes whose dna Dept. H had access to.
At the time I read Vol.2 I thought Flex was Jeffries' 'child' until seeing Seagle's interviews online.
But the Flex as Wolvie's son isn't canon so it's all speculation untill it's in print.