There is no difference of pronunciation between "ces" and "ses". They are homophones.
Okay, I've got a different question that I'm surprised no one else has raised. There's some savoir/connaitre distinction going on in some of these exercises and normally the latter applied to people is being translated as "know": "I know this kid" / etc.
What is it about this sentence that excludes "know" and requires "understand"? Is there something magical about it being the "nous" subject? Is it because the object is plural? Why exactly is "We know these kids" unacceptable here?
I do not think that the verb "comprenons" could be translated as "include" in this specific sentence for two reasons (which I think also apply in English):
When the verb "comprendre" means "to include", you should precise in what they are included. Context is needed to use this verb in this way.
When the verb "comprendre" means "to include", the subject has to be either what is included or in what something is included.
So, if you want to give the verb "comprendre" the meaning of "to include", you should reformulate the sentence above: #"Nous comprenons ces gamins." -> "Ces gamins sont compris dans le groupe." ("These kids are included in this group.") or "Ce groupe comprend des gamins." ("This group includes these kids.")
For these reasons, I do not think that "comprenons" could be translated as "include" in the sentence of this topic, but rather by "understand".
I hope that my explanation was clear enough and helped you. If not, feel free to ask me to rephrase it. I am still learning English, so I will not be offended if you tell me that I said something wrong :)
I didn't risk it (Duo can be agonisingly fussy) but I would have thought that 'youngster' would be ok for 'gamin(e)' - Linguee gives this as a valid translation.