OK, devil's advocate?
Does he want more time with the kids? But you won't agree? So agree to more time with the kids, get less child support and he can spend the child support he doesn't give you on clothes. Yup, didn't think so.
Or he agreed to the current set of arrangements. Supply the clothes, foster good will. Do the clothes get worn out more at his place than at yours? If the answer is yes, then maybe you ought to do more with the kids, after all if the clothes are getting worn out more at his place with 15% care than at yours with 85% then you need to get out more.
Child support don't have any rules BTW - so no one here can tell you a definitive answer. There are no rules.
So let me give you some options.
So - Plan A - supply clothes - live a less stressful life, stress less, live longer... (my preferred option).
Plan B - Don't supply clothes, but be reasonable and tell him 2 weeks in advance to prepare.
Plan C - Don't tell him and be a completely nasty piece of work... Just drop them off in the clothes they are wearing. This is stupid.
Nope, there is a Plan D. Even more stupid.- my ex did this one... Met me at McDonald's and insisted on going into the disabled toilet, so we could take 'her' clothes off the kids, and put on 'my clothes' . So she told me I had to bring clothes to change over - go into a toilet with her to change the clothes of 3 kids... Madness.
So what you do is up to you? Kids clothes are cheap and I like Op-shops. She sends kids in rags. So I start shopping for clothes when I don't have the kids... They start rocking up to my house to find nice new clothes and they are grateful. So it didn't help her cause as far as the way the kids chose to perceive her behaviour...
Final thought - be reasonable and look for reasons not to have arguments. Why?
Story time - prior to the McDonald's, stupidity mentioned above. My ex would send the kids in stupid clothes, gum boots. A shirt on 4-year-old with two stupid looking dogs with the writing 'like father, like son'. It was a stupid game to her - the game was called how to hurt me...
So these days the kids live with me and they remember the stupidity.
My opinion - with 85% care you're getting the maximum child support. If you really wanna have this argument - then do it this way. Tell the ex you would like to enter into an agreement with him. Under the agreement, he needs to provide clothes for the kids when they are with him. Consequently, you will agree to 10% less child support per fortnight.
Yup, didn't think so.
Learn to argue less. Live more.