Welcome to disABILITIES.
If you think the scooters would help then rent them. I haven't done that yet as I find them to be cumbersome and I can walk (and need to for exercise).
That is good advice in general, but WDW parks won't rent scooters (
ecvs) to be driven by people under 18 and the websites of most of the outside rental places also indicate that they will only rent for adults.
If they get very tired, you may need to rent wheelchairs for them (although getting a teenager to admit to being that tired is probably not going to happen).
Will you be driving a car and do you have a handicap parking tag? I usually drive so I don't have to wait on buses. I ask the parking attendant if I can park in the first spot instead of way down a row so it's not so far to walk to the tram.
The handicapped parking are at AK and the Studio are close to the entrance. Handicapped parking at Epcot is a fair hike. There are no parking lot trams from the handicapped parking area in any parks. The tram from the parking lot always brings you as close as possible to the actual park entrance, so the best advice might be to tell each parking CM that you get to that you have people with mobility issues and ask to park close to the tram stop.
If you are staying on site, it's best to take the bus (unless you are staying at a MK resort and can take the monorail or boat). The bus stop area is very close to the park turnstiles. If you drive and park in the parking lot, you will need to take the parking lot tram to get to the TTC, then take the monorail (up a long, steep ramp to get to the station) or boat to get to the same are where the bus lets you off. Most of the bus stops do have benches for use while waiting for the bus, so you almost never have to stand the whole time.
You might want to check into the GAC (which I think stands for general assistance card). There more data on this board about them. I do not use one so I don't have any information about them.
GAC is an abbreviation we use of the boards for Guest Assistance Card. It is a tool for CM to be able to tell what sorts of assistance is needed by someone with invisible disabilities. People who have wheelchairs or ecvs (or visible disabilities) generally don't need a GAC unless they also have invisible disabilities that are not taken care of by having a wheelchair accessible line. Examples of things a GAC would be used for include: a quieter place to wait (for someone with autism or sensory issues); to be able to bring a stroller into lines and use it like a wheelchair; being able to wait in a shaded spot if the queue is in the sun for a significant amount of time(although most queues are shaded). WDW doesn't generally give out GACs for conditions involving stamina. For stamina or tiredness issues, WDW's official publications suggest using a wheelchair or
ecv and use of fastpass, since the time and distance spent in lines is smaller than the time and distance it takes to get from place to place.
WDW is a very large place, which most people don't fully appreciate until they are there. Just to walk around the lake in WS is over a mile, and the average person probably walks between 6 and 9 miles a day. Most of the walking is not in lines. If you walked that much all at once, it would be impossible. That's why pacing is very important.
Using fastpass is a good idea. You can send one member of your party ahead to get the fastpasses - You put your park tickets into the faspass machine. A fastpass pops out with a return time printed on it. When you return at the time, your wait in line is generally going to be 10 minutes or less.
Also, if you vcan get to the parks early, you can go on a lot of rides in a very short time without doing a lot of running around. When DH and I went in July (normally a busy time), we were able to go on about 8 things in MK before 11.
This is a very good website with a lot of information and resources about visiting WDW with disabilities or challenges. She has some hints for pacing, etc in the FAQs area.