As Talking Hands already said, either First Aid or Baby Care Centers would be good, cool places to feed or give treaments to your child. If you want to leave any of your medical equipment, they will store it for you in First Aid. Either of those places are also cool, quiet places to rest (or just get away from all the commotion). Their location is marked on the park maps and you don't need a GAC or anything special to use either place.
GAC is the abbreviation we use on these boards for Guest Assistance Card so we don't have to type so much.
First, what it isn't:
It's not a pass, doesn't shorten or eliminate waiting in line, isn't meant to give any advantage or special treament to someone with a disability, and it isn't given just because someone has a specific diagnosis. Some people think all GACs are the same, but they are not.
What it is:
A tool to let CMs know what sorts of assistance/accomidation are needed by a person with a disability, especially an invisible disability.
In most cases, someone using a wheelchair or
ecv, crutches, cane or has a cast doesn't need a GAC. That's because the CMs can see that they need an accessible line/entrance. There may be a need for a GAC if there are other needs besides the need for an accessible line (or CMs are not noticing the need).
It is based on needs and the "message" printed on the GAC reflects the needs. To request one, go to Guest Services in any park with the person with a disability. Explain the needs; no need to go into detail regarding diagnosis. Because even people with the exact same diagnosis might have very different needs, the messages stamped on each GAC is different, based on the needs.
As ducklite mentioned, just because you have a GAC doesn't necessarily mean that every attraction can provide that accomidation. For example, some attractions are outside, so they can't provide an air conditioned indoor space. Also, the time spent outside of attractions/queues is going to be at least as long as the amount of time spend
in attractions. So other strategies to avoid heat/sun are important.
If you can go when it's cooler and during non-peak times, that will help a lot. Also, even during busy times, you will avoid the hottest part of the day and the biggest crowds if you can be at the parks right at opening.