2 people I know were in a car accident 10 days ago. One is 8 and one is 11. They are in the hospital and both had skull fractures. One had a collapsed lung. About how long will they be in the hospital?

Really depends on just how well they respond to treatment.
This is really a question for the treating physician.

Not even 100 doctors online can answer that, sorry.
There are too many variables.
Ask the family, or if you are allowed to visit, ask the staff for a guess. Even they probably won't predict.

They're responding well. Could it possibly be months? I just wanted to get a round about idea.

Even the attending doctors and nurses don't know.

It depends on residual problems, if there has to be rehab, and maybe they will have problems for the rest of their lives.

Even though I don't think you are understanding how this is impossible to give 'a round about answer,' if the doctors said that they are responding well, then hopefully that means that it won't be months.
It sounds like you have asked people close to the situation and that's all you are being told. You need to realize that many, many conditions, especially major injuries like this, DO NOT have an early prognosis, regardless of how many people you ask. Please respect the need to wait.