Everybody is entitled to their own view and judgement and I maintain my earlier one - the mother should not be judged negatively if she chooses not to provide clothes.
Legally is not her responsibility, morally, as long as the father is capable of buying for himself and washing for himself I don't see any possible excuse for him not to do it for his own children. And if it is the father that fails in his duty for no good reason, than it shouldn't be the mother held responsible for his failure.
I don't agree with the minimizing of the expense and effort involved either - say a long weekend - Fri to Mon = 3 kids x 3 outfits = 9 outfits. Perhaps for a sahm it's no big deal but for someone working full or part time and looking after 3 kids for most of the time it may be the only chance to get an hour off the wheel. As for the costs, it is up to OP to judge if providing clothes for the time with their dad will financially impact her.
Yes, for the kids sake we should seek peace and make compromises but compromises should be made on both sides. It doesn't mean that if, for example, an ex is willing to be petty and demanding towards their fellow parent, either out of laziness or even to control and humiliate them, the default answer is to give in and satisfy the demands. Often, this leads to a continuation (after the break-up) of a faulty marital relationship with all its original negatives, including the impact on the children.
It is up to the OP, imo, to judge what is morally right, both for herself and for her children, and if, for objective reasons, she finds the demands unfair, she should at least try to do what is right for herself. The chances are that the father will just get on with life and fulfill his responsibilities, even though his default position was to place all the child related chores on his ex partner.