Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
2- If you mean that diaper change involves touching something that is impure, this does not affect your wudu’ either.
Answering your question, Sheikh `Abdullah ibn Jibreen, a prominent Saudi Muslim scholar, states:
If someone touches somebody else’s private parts with lust, then that invalidates his wudu’. However, there is a difference of opinion when such touching is not accompanied with lust. The strongest opinion is that touching the private parts of a baby in order to clean the baby does not nullify wudu’ because such is not a cause of sexual desire.
Furthermore, it is something that almost all people have to go through and if it were to nullify wudu’, it would cause great hardship. And, if it did nullify ablution, this would have been well-known among the Companions and those who came afterwards.
Excerpted, with slight modifications, from: www.islamtomorrow.com
Sheikh M. S. Al-Munajjid, a prominent Saudi Islamic lecturer and author, adds:
As for changing a baby’s diaper, if you mean the act of changing itself, this does not affect the validity of one’s wudu’.
If you mean that it involves touching something that is impure, i.e., the baby’s urine and stools, this does not affect your wudu’ either, because there is no connection between touching something impure and the validity of one’s wudu’. It has been reported that there is scholarly consensus on this point, as stated in the book Al-Awsat by ibn Al-Mundhir (1/203). All one has to do is to wash his hands to get rid of any impure material.
If you mean that it involves touching the child’s private parts, whether the child is a boy or a girl, in the case of a child under the age of two years, the rulings on `awrah (that which is to be covered) do not apply, as the scholars have stated, so if you touch them, this does not affect your wudu’.
Almighty Allah knows best.
Excerpted, with slight modifications, from: www.islamqa.info