A secondary source would be the English Sefer "Summary of Halachos of the Three Weeks" by Rabbi Shimon Eider zt"l, chapter III D on page 9.
You can see it here with all the sources: http://books.google.co.il/books?id=k2lV5wQwwj0C&lpg=PP1&hl=iw&pg=PA9#v=onepage&q&f=false
Here is a copy of the relevant chapters - without the sources (which are in Hebrew and time consuming to type).
HALACHOS OF THE THREE WEEKS - Ch III D
3. A Jew cleaning clothing of a gentile
A Jew may clean or launder garments of a gentile during the Nine Days-but should refrain from cleaning their garments in public during
the week Tisha B'Av occurs.
4. Only one garment
If a person has only one garment and it requires cleaning or laundering, or if he has many but all are dirty, it is permissible to
clean a garment until the Shabbos before Tisha B'Av, but cleaning is
prohibited during the week in which Tisha B'Av occurs.
6. Washing children's clothing
Washing children's diapers and clothing are permissible even in the week in which Tisha B'Av occurs. This halacha applies even to children
whop do not wear diapers but who constantly soil their clothing with
dirt, mud and the like. Washing these garments, however, should be
done in private.
7. Washing for the purpose of a mitzvah
Washing for the purpose of a mitzvah is permissible-even during the week in which Tisha B'Av occurs. Therefore, a woman who is required to
wear white for the Seven Clean Days may wash her garments and sheets
for this purpose. On Tisha B'Av, however, if she discovers that she
has no clean white garments, washing her garments is prohibited; she
should wear a clean (i.e. without stains)-even colored