A number of eminent Acharonim write that it is important to ensure that even small children, who have not yet reached the age of understanding (gil chinuch), wash their hands in the morning. The reason for this is that if they don’t wash their hands, the food they touch will become ruined by the ruach ra’ah that is upon them (Chida; Pri Megadim, Mishbetzot Zahav 4:7; Mishnah Berurah 4:10). Additionally, there are those who abide by the extra pious act of washing a newborn baby’s hands, as the Ben Ish Chai (Toldot 10) writes, for by doing so, the children are raised with purity and sanctity.
However, in practice, many people are not strict about the washing of their children’s hands three times after they wake up, because according to some prominent Acharonim, the ruach ra’ah only lingers on the hands of one who is at least thirteen years of age. The more a person can connect to holiness and act to repair the world, the more the evil spirit contrastingly strives to make him impure. Hence, the ruach ra’ah does not rest on the hands of gentiles, for they are not obligated to perform mitzvot. Similarly, concerning children, the ruach ra’ah does not rest upon them in its full force until they are sanctified in the obligation of performing the mitzvot. Still, we are commanded to educate minors to perform the mitzvot, and once they start observing the holy commandments, the ruach ra’ah slightly lingers upon them as well. Therefore, from the time they reach the age of understanding and are capable of comprehending how to wash their hands, one is obligated to educate them and accustom them to washing (based on Shulchan Aruch HaRav Tinyana Edition 4:2; Eshel Avraham Butshatsh 4:3; Tzitz Eliezer, part 7, 2:4).
In conclusion, it is a mitzvah to accustom children from the time they reach the age of understanding to wash their hands three times after sleeping, and it is an obligation to wash their hands starting from the age of mitzvot, meaning thirteen years old for a male and twelve for a female. There are those who are stringent to wash their baby’s hands from the time he can touch food (Mishnah Berurah 4:10). Additionally, there are individuals who enhance the mitzvah by washing their baby’s hands starting from the time of his brit milah, or even from birth, for even then Israel’s unique holiness begins to appear (as brought in parenthesis in Shulchan Aruch HaRav there; see Kaf HaChaim 4:22 as well).