Cursed in their hearts

Not in the grossest sense of the expression, so as to deny the being of G-d, and wish there was none, and conceive blasphemy in their hearts, and utter it with their lips.
But whereas to bless G-d is to think and speak well of Him,
Ascribe that to Him which is His due;
So to curse Him is to think and speak irreverently of Him, and not to attribute to Him what belongs unto Him.
Thus man might fear that their sons/daughters, amidst their feasting, might boast of their plenty, and of the increase of their substance, and attribute it to their own diligence and industry, and not to the providence of G-d, of which a parent feared they might speak slightingly and unbecomingly, as persons in such circumstances sometimes do.
One may little blessed G-d in their hearts is not blessing Him as they should, but was interpretatively cursing Him. The Hebrew word used properly and primarily signifies to bless, and then the meaning is, either that one’s sons & daughters had sinned, but took no notice of it, nor were humbled for it, but blessed G-d, being prosperous and successful, as if they had never sinned at all.
This is a lesson to learn, whether it is our offspring’s or our own doing; one much teach and intercede for others what is considered a blessing or a cursing. If we do not think and speak well of our Heavenly Father and give Him all the glory, we are cursing Him. All we have or will obtain is His blessings to us. He gives us the ideas or knowledge how to increase our blessings.
Watch therefore that you do not curse in word, thought or deed; not even in your heart. And yes, we are our brothers/sisters keepers; so interceded for them.