Hebrew word is "ילדיו" which is "his offspring" and is male plural. This is basically the masculine plural participle of his "begats."
In other contexts this could be more generally pointing to all of his children (including Dinah), but the text seems to imply that it's only speaking about sons since it uses the number 11 specifically.
Benjamin isn't born until after he wrestles with the mysterious figure in the night and is renamed Israel. Though the text doesn't call him Israel until just after Rachel dies in childbirth.
What are the significances of this? If we think about this as an etiological narrative, we might see Benjamin as somehow set apart from his other brothers. Jacob, for example, was also the youngest of the twins and received the blessing over Esau.
If we look forward and see the first king, Saul, a Benjaminite, we might see either a legitimation of him as the product of his father being blessed and renamed, or we might see him as set apart from his other brothers as problematic since we know that Saul is a failed king who is deposed by David.
I find it useful to project the later history of the tribes back onto the sons of Jacob as they seem to act as archetypal patriarchs representing the various tribal group identities. This can help us understand who the power players were behind the pen of the text.