First of all, please make sure you actually visited our Support Procedures page.

Your issue here is a very basic python type mismatch. I know that dealing with some 3rd party APIs and leaky documentation can be frustrating and at some point even obvious things can be perceived as impossible, but

We cannot provide support on learning C++, Python, or one of their popular third-party libraries.

Regarding your question. The issue here is that you're trying to insert the list of objects list[c4d.BaseObject] using function InsertObject() that only expects a single object. You need to iterate your list of objects, e.g. using for loop:

for child in children:
    GroupList.InsertObject(child, 1)

A couple more things about your code.

1. Calling c4d.EventAdd() is useless from within the Python tag, as mentioned in the documentation, it does nothing in this case
2. Populating your InExcludeList every time the python tag is executed is not ideal (it's slow!). Hence, you'd need some smarter way to distinguish when you need to repopulate the list and when it is not necessary. There's at least one thread about it, where Maxime mentioned this issue: Execute python tag only when hierarchy changes. Please check the code snippet below that implements a very draft way of doing so, simply by comparing the number of children. Ideally, you need to keep track of the entire children list and do actual comparison there, but this can be redundant depending on your goals.

There's one another thing. Please do not give up old threads and start new ones instead, this only makes more clutter on the forum and doesn't help with processing your questions. Hence I've resurrected your previous thread. For your future threads please consolidate your consequent answers in a single posting and do not duplicate threads.

Cheers,
Ilia

Python tag script (to be inserted on a Group effector):

import c4d

doc: c4d.documents.BaseDocument  # The document containing this field object.
op: c4d.BaseTag # The Python tag containing this code.

childrenCount: int = 0  # keep number of children globally between main() calls

def main() -> None:
    global childrenCount
    obj: c4d.BaseObject = op.GetObject()

    children: list[c4d.BaseObject] = obj.GetChildren()
    if childrenCount == len(children):  # early exit if number of children hasn't changed
        return

    childrenCount = len(children)
    print('Updating InExclude list')

    inexcl = c4d.InExcludeData()
    for child in children:  # Process children one-by-one
        inexcl.InsertObject(child, 1)

    obj[c4d.MGGROUPEFFECTOR_EFFECTORLIST] = inexcl