Admission for teens to Paris sites

they will just walk in with you except at the Arc de Triomphe and Invalides. The long lines however ARE the security lines. Many places have shorter security lines for ticket/pass holders but everyone goes through the same lines at the Louvre and at Versailles. At Versailles you will skip the ticket line after the very long security line. At the Orsay you can use a different door/line for security if you have tickets (and that is well worth planning ahead). I'd probably get the museum pass given your agenda and would not buy it ahead (and pay big delivery fees) but just get it at the first museum or at the airport. Don't make the Orsay your first stop -- most of these are other places do not have enormous lines.

Thank you! You said, "they will just walk in with you except at the Arc de Triomphe and Invalides." What happens there? Do I stand in the ticket line for the girls and then move to the security line?

Yes at the Arc and Invalides, the kids have to get tickets -- they are free but they need to line up to do so. Lines are rarely a big deal here though -- it isn't like the 2 hour d'Orsay line. You will also use a special designated line a the Orangerie which helps if there are long lines there which there sometimes are. Again -- with so many museums on your list, I'd get the museum pass. At the Louvre sometimes Museum Pass holders can use the Richelieu entrance which is shorter. This is somewhat variable.