Can I give my 2 & 4 year old Children's Robitussin even though it says not for children under 6

No. 2 and 4 are under 6. Talk to your doctor about your need to stop their coughing (or whatever concerns you).

I agree... even though their ages add up to six... neither one is six yet. And it has to do with the pain reliever being dangerous to some kids under six.

I agree with the above. The guidelines on the medication are for the safety of your children. It's not safe to give that medication to a child under the age of 6, therefore I wouldn't give them that medication.

There are other medications for toddlers and young children under the age of 6. I'd go to your pharmacy and ask the pharmacist for a medication that would be appropriate for a 2 and 4 year old, or I'd see take them to see their doctor.