Question: While I’m washing my children’s clothes on chol hamoed, can I throw some of my own clothes into the washing machine?
Answer: The Gemara (Moed Katan 14a) writes that in order to ensure that people would prepare properly for yom tov, chazal instituted that it is forbidden to wash clothes on chol hamoed.
Thus, the Shulchan Aruch (OC 534:1) writes that under regular circumstances one mustn’t wash one’s clothes on chol hamoed. The Rema, however, writes that one may wash young children’s clothes if they constantly dirty them. The Mishna Berura (534:11) explains that one can only wash children’s clothes that they’ll need for that yom tov.
R’ Ovadia Yosef (Yabia Omer 7:48:1), R’ Ephraim Greenblatt (Rivevos Ephraim 1:354) and R’ Yehoshua Neuwirth (Shemiras Shabbos Kehilchasa 66:63) write that as the reason for this prohibition is to ensure that people are well prepared for yom tov, it doesn’t make a difference how one washes their clothes. Thus, one can’t wash adult’s clothes in a washing machine. Likewise, R’ Moshe Feinstein (Igros Moshe 5:36:1) writes that one can’t give one’s suit in to the dry cleaners.
The Mishna Berura (534:4) quotes the Chayei Adam who permits washing handkerchiefs that need washing regularly. Based on this, R’ Yehoshua Neuwirth (Shemiras Shabbos Kehilchasa 66:66) allows one to wash underwear on chol hamoed providing that they washed everything before yom tov (See Shevet HaLevi 8:124).
In conclusion, while one may wash young children’s clothing, etc. on chol hamoed, one may not add any regular clothes to the wash at the same time.