All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
It is a good thing that you fear for the safety of your children and seek the means to achieve that, as this is religiously required. There is no harm in the moderate natural fear for the children; rather, this is a manifestation of the mercy that Allah places in the parents' hearts towards their children. It was authentically reported that ʻUmar ibn Al-Khattaab, may Allah be pleased with him, said, "The Messenger of Allah, sallallahu ‘alayhi wa sallam, said to us, '...Do you think that this woman would ever throw her child into the fire?' We said, 'No, by Allah, not when she is able not to throw him.' Thereupon, the Messenger of Allah, sallallahu ‘alayhi wa sallam, said, 'Verily, Allah is more merciful to his slaves than this woman is to her child.'"
Moderate fear for the safety of one's children is praiseworthy. However, if it exceeds moderation due to Waswaas (obsessive thoughts) and illusions, it becomes blameworthy. It is a kind of disease that requires therapy, and it seems that you suffer from it. So try to get rid of it lest you incur inconvenience and hardship on yourself and others.
We believe that the solution is easy. First of all, whenever you experience such fears, you should remember Allah by saying Thikr (expressions of remembrance of Allah) in order to attain serenity and relieve your anxiety. Allah, the Exalted, says (what means): {Those who have believed and whose hearts are assured by the remembrance of Allah. Unquestionably, by the remembrance of Allah hearts are assured.} [Quran 13:28]
Secondly, supplicate Allah in favor of your children frequently to bless them with safety, protection, and well-being. Verily, the supplication of the parents for their children is answered. Abu Hurayrah, may Allah be pleased with him, narrated that the Prophet, sallallahu ‘alayhi wa sallam, said, "There are three supplications that will undoubtedly be answered: the supplication of one who has been wronged, the supplication of the traveler, and the supplication of a parent for his child." [Ibn Maajah]
Thirdly, if you happened to be separated from them for any reason, you should entrust them to Allah, for He is the Protector. Ibn ʻUmar, may Allah be pleased with them, narrated that the Prophet, sallallahu ‘alayhi wa sallam, said, "Luqmaan Al-Hakeem (the Wise One) used to say to his son, 'Verily, Allah guards whatever is placed under His protection.'" [Ahmad]
Fourthly, you should adhere to Taqwa (piety and mindfulness of Allah) and perform many righteous deeds so that Allah would protect and guard your children. He says (what means): {And let those (executors and guardians) fear (injustice) as if they (themselves) had left weak offspring behind and feared for them. So let them fear Allah and speak words of appropriate justice.} [Quran 4:9] Muhammad ibn Seereen a leading imaam from the Taabiʻoon (generation following that of the Companions), said to his son, "O my son! I prolong my prayer for your own sake so that Allah would guard you (as a reward for my worship)." He then recited the verse: {... and their father had been righteous.} [Quran 18:82]
Fifthly, if necessary, you may consult a trustworthy psychiatrist; this could help you overcome such fears.
Allah knows best.