From the perspective of privacy education, it is preferable that the mother changes the child’s diaper whenever possible. (Privacy Education-1 | Psychological Counselor Kerem Şahin – Hizmetten)
Taking this into account, the general approach may be that the mother assumes this responsibility primarily, while the father may assist when needed. In cases of necessity, other family members may also carry out this task. (Can an older brother change his younger sister’s diaper? | Hikmet.Net)
Since there is no explicit statement in the primary religious texts regarding the private parts of small children, scholars have drawn a framework based on general principles. Accordingly, it has been stated that there is no harm in changing the diapers of children who are still at such an age or in washing/bathing them.
However, once children reach a certain age (generally after around 7–9 years old), they should perform their personal hygiene themselves. Unless absolutely necessary, no one should look at or touch their private parts, even for cleaning purposes.