Does informing people that one is performing the Sharia-compliant fortification (tahsin) of children or oneself with the prescribed dhikr affect this fortification, thereby invalidating it? And does informing people about things that happen to a person and that others wish for affect him? And what is the ruling on informing about such matters?

Your informing people about the protective measures you have taken for your children does not affect Allah's preservation of them, for no one can repel Allah's preservation. Allah Almighty says: "And if He intends good for you, then none can repel His favor." Speaking of blessings as a form of gratitude is commendable, but if you fear the evil eye, it is better to conceal them, as Ya'qub said to Yusuf: "O my son, do not relate your vision to your brothers, lest they concoct a plot against you."