A simple Vue wrapper component that let you add classes to all children.

ChildClasses.vue

<script>
export default {
  name: 'ChildClasses',
  functional: true,
  render (h, ctx) {
    return ctx.children.map((vnode, index) => {
      let { tag, data = {} } = vnode
      let props = ctx.props
      let children = vnode.children
      let on = data.on || {}
     
      const classes = [
        data.class,
        ctx.data.class
      ].filter(Boolean)

      const staticClass = [
        data.staticClass,
        ctx.data.staticClass
      ].filter(Boolean).join(' ')

      if (vnode.componentOptions) {
        tag = vnode.componentOptions.tag
        props = vnode.componentOptions.propsData
        children = vnode.componentOptions.children
        on = vnode.componentOptions.listeners
      }

      return h(tag, { ...data, class: classes, staticClass, on, props }, children)
    })
  }
}
</script>

ExampleUsage.vue

<template>
  <ChildClasses class="mr-5">
    <!-- All children inside slot will get a .mr-5 class -->
    <slot />
  </ChildClasses>
</template>