If you haven't looked at it yet, check out the disABILITIES FAQs thread near the top of this board.
What you are asking for isn't really a Pass, it's a card that tells the CM (Cast Members) what sort of assistance you need.
It is called a Guest Assistance Card (and we abbreviate it as GAC). There is information about GACs in the disABILITIES FAQs thread. Even though it was written about WDW (Disney World), how you get a GAC works basically the same at
Disneyland. There are some differences because Disneyland is older and less accessible than WDW, but it's basically similar.
The GAC is not meant to shorten your wait in line, but to provide accomidation for your needs. You explain what your needs are and the CM stamps a message on the GAC that should help meet your needs. The GAC is issued to the person with a disability (so you are the one using it), but your family will be able to accompany you when you use it.
In most cases, where people have trouble with walking and/or standing, they will recommend an
ECV (electric
scooter) or wheelchair. Since you are planning to be alone with a 6 month old and a 5 yr old, that won't work.
Some people find that pushing a stroller helps them because they can lean on it a bit and take some stress off of the back. I don't know if that is your situation. Strollers are not normally allowed in lines. That is going to cause a problem for you, since I'm assuming you probably can't carry the 6 month old for long without back pain. I know that at WDW, there is a GAC that allows strollers to be used in lines the same as wheelchair. I am not sure if Disneyland does that, but if they do, it would be helpful to you.
You've probably already seen
this thread about the GAC at Disneyland, but if you haven't, check it out.
