I think I found the right syntax (it seems to be working as I expected):

response = xmltodict.parse(xml, force_list=('Child','Brother'))

Just posting in case anyone would look for the same answer in the future.

You can pass a postprocessing function to xmltodict, which allows you to modify the dict values.
But postprocecssing needs to return a key and a value:

import xmltodict
import json


def postprocessor(path, key, value):
    if key == 'Pokemons' and not value:
        return key, []
    return key, value

xml = """<Something>
    <Guitar>
        <name>Walden</name>
        <strings>5</strings>
    </Guitar>
    <Pokemons>
    </Pokemons>
</Something>"""


res = xmltodict.parse(xml, postprocessor=postprocessor)
print(json.dumps(res, indent=2, sort_keys=True))

Output:

{
  "Something": {
    "Guitar": {
      "name": "Walden",
      "strings": "5"
    },
    "Pokemons": []
  }
}

This problem is discussed in this issue on Github. The xmltodict package now supports

d = xmltodict.parse(s, force_list={'car'})

Although this still doesn't create an empty list if the field is absent.

Try a flatten function on the "episodes" key?

def flatten(it):
    res = []
    for item in it:
        if not isinstance(item, list):
            res.append(item)
            continue
        res.extend(item)
    return res

This is a common problem with xmltodict, which was discussed here:

• xml containing 1 child

The workaround to this behavior would be to use a force_list option (available in the master branch at the moment):

xmltodict.parse(data, force_list={'books': 'book'})