Albert Barnes Commentary 1 Thessalonians 2:7

"But we were gentle in the midst of you, as when a nurse cherisheth her own children:" — 1 Thessalonians 2:7 (ASV)

But we were gentle among you, etc. Instead of using authority, we used only the most kind and gentle methods to win you and to promote your peace and order. The word here rendered 'nurse' (a term that can also convey 'cherisheth' or the role of a 'nursing mother') may mean anyone who nurses a child, whether a mother or another person. It seems here to refer to a mother (1 Thessalonians 2:11).

And the idea is that the apostle felt for them the affectionate solicitude which a mother does for the child at her breast.