clarification on Eiffel Tower

Yes, you can get a ticket to the top when you are on the 2nd level. You can get an advance ticket for the elevator to the 2nd level and then purchase the ticket to the top from there. If you're ambitious and want to climb to the 2nd level you don't need to buy a ticket in advance, just get it at the ET when you get there, the line for the stairs is usually quite short.

Thanks! How difficult are the stairs? We have a 5 year old, plus a post-knee-surgery man who is generally fit, but stairs are not his favorite.

Agree with Nancy's advice. Also, a big advantage of not buying tix in advance is that you can go when convenient and when weather is good. You don't say how old the kids are, but we find it more fun / more of an adventure to walk up (you can still take elevator down for free if desired). As far as the top level... the 2nd level is very high; we went once to top level and didn't feel it was worth it; hardly any different from 2nd level. Enjoy your trip!

The stairs are not 'difficult', but there are a LOT of them, as you can imagine to get to that height. A high energy 5 year old could make it with some rest stops. As far as a post-knee surgery, I think he should take the elevator.

You didn't say that anyone in your party is afraid of heights but it's something to keep in mind. The stairs are rather open. You are well aware of how high up you are. This is far from a universal problem but it could be an issue for some people.
When we were there last I took the elevator down from the second floor to the first but it wasn't possible to go back up via the elevator, so I had to take the stairs. It was a white-knuckle affair for me but it was clearly not an issue for the others who passed me in both directions, laughing and having a great time.
As for the top vs the 2nd floor, I think your children will like going to the top. It's interesting and something our granddaughters thought well worth doing. I agree with Bob from Minneapolis that the second level is plenty high but I really think the top is a treat for kids.

Thanks, all! None of the adults are scared of heights, and the 5-year old would be the only question mark on that front. I'll discuss with my husband who is the one with the bum knee. This is an extended family trip with 5 adults and 4 kids aged 5, 9, 10, and 11.

I appreciate the advice.

Playing it by ear has other advantages, too : there might be two busloads of people from the same tour group all there straining for a selfie against the same railing at once, like fishermen about to tip over a party boat, and then 15 minutes later you might have the place to yourself during a lull.

I battled my fear of heights--really more about the ascension than being up there--and once I realized I felt fine about the 2nd level decided to go all the way to the summit. The views weren't substantially different, to me, really more about having the complete experience. I only took the stairs down from 2 to 1, people coming up were moving at various paces, there's enough room and landings to get off to the side if anyone needs a rest.

Thanks again for all the advice. One other question: if we walk up, can we take the elevator down without a ticket? My husband's knee is worse on descent than ascent and he thinks he can handle the climb.