With the help of @markerikson author of:

http://redux.js.org/docs/recipes/reducers/ImmutableUpdatePatterns.html

I was able to update that deep level of nested data:

The object to update are the all objects under "children" property of this object:

 state: {
    "1": {
      "show": false,
      "description": "one",
      "children": {
        "1": { "show": false, "description": "one" },
        "2": { "show": false, "description": "one" }
      }
    },
    "2": {
      "show": false,
      "description": "one",
      "children": {
        "1": { "show": false, "description": "one" },
        "2": { "show": false, "description": "one" }
      }
    }
  }

And the code to update it is:

let newState = {};
newState = { ...state, newState }

for (var childKey in newState[appClassId].children) {
  newState = {
    ...newState,
    [appClassId]: {
      ...newState[appClassId],
      children: {
        ...newState[appClassId].children,
        [childKey]: {
          ...newState[appClassId].children[childKey],
          show: !newState[appClassId].children[childKey].show
        }
      }
    }
  }
}

I would recommend leaning on a utility library like lodash.js in addition to the spread operator if you're doing anything more complex than assigning a value or two.

Assuming that the number of appClassIds inside state and children inside each appClass are completely dynamic:

import { reduce } from 'lodash'

const newState = reduce(state, (modifiedState, appClass, appClassId) => {
  const { children } = appClass
  // toggle show for each child (non-mutating)
  const toggledChildren = reduce(children, (newChildren, child, childId) => {
    return {
      ...newChildren,
      [childId]: { ...child, show: !child.show }
    }
  }, {})

  // persist modified children within the appClass
  return {
    ...modifiedState,
    [appClassId]: {
      ...appClass,
      children: toggledChildren
    }
  }
}, {})

Hope this helps!

try this:

const originalChildren = state[appClassId].children;
let updatedChildren = {};

for (var child in originalChildren) {
   if (originalChildren.hasOwnProperty(child)) {
      updatedChildren = {
        ...updatedChildren,
        [child]: { ...originalChildren[child], show: !originalChildren[child].show }
      };
   }
}

const newState = {
  ...state,
  [appClassId]: {
    ...state[appClassId],
    children: { ...originalChildren, ...updatedChildren }
  }
}