All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Whoever has taken a vow to do or not to do something isn`t obliged to fulfill it nor is he obliged to offer an expiation, as indicated in the Hadith narrated by Ibn Abbas: While the Prophet (PBUH) was delivering a sermon, he saw a man standing, so he asked about that man. They (the people) said, "It is Abu Israil who has vowed that he will stand and never sit down, and he will never come in the shade, nor speak to anybody, and will fast.'' The Prophet (PBUH) said, "Order him to speak and let him come in the shade, and make him sit down, but let him complete his fast."{Bukhari}.
In the afore Hadith, the Prophet(PBUH) didn`t order that man to offer an expiation; rather, he ordered him not to fulfil his vow. This shows that a person isn`t obliged to fulfil a vow to do something permissible; especially, if it causes extreme hardship. However, if he took a vow to do an act of obedience and righteousness such as fasting, then he is obliged to fulfil it, and this is why the Prophet(PBUH) said:".....let him complete his fast."
Accordingly, the vow you made to kiss your son`s head and feet isn`t among the acts of obedience; rather, it is among the permissible acts, so fulfilling it isn`t obligatory.
"If a person vowed to do or not to do something permissible such as eating and sleeping, e.g he vowed not to eat sweets, then their vow it isn`t considered binding. This is based on the Hadith narrated by Abu Dawoud, and reads as follows: "There is no vow except in an act which seeks the pleasure of Allah, the Exalted"….The correct opinion is that no expiation is to be offered for that vow because it isn`t effective."{Moghni Al-Mohtaj, 6/235}.
In conclusion, the person who made the above vow(questioner) isn`t obliged to fulfil it. And Allah knows best.
