These moms aren’t confused about remembering. They get confused when they try to remember, but the confusion is about which number is which (“confused about remembering” would mean that the concept of remembering is confusing). The way you’ve described the situation in the question is much clearer than what you’ve written in the passage, so you could just leave it as you had it there:
[Most] beginner moms find it difficult to remember all of the numbers related to their baby.
Here’s how I would combine “confused” with “remember” if you still want to do that:
Most first-time moms get confused
about (when they are) trying to remember all the numbers related to their babies.
Most first-time moms get confused trying to remember all the numbers related to their babies.
The verb “remember” describes the action of recalling something more or less accurately, so we have to include something that indicates the partial failure of that action. I’ve chosen “trying”.
You may also notice that I’ve written “get” instead of “are”. This is because we are not describing a persistent state, but rather a temporary state that occurs at the moment of remembering.
“Confused” by itself means the person knowingly or unknowingly thinks the wrong numbers or no numbers at all. Since thinking of a number and remembering it are basically the same thing, we could leave out any mention of remembering and just write it this way:
Most new moms get confused about
remembering all the numbers related to their babies.
Most new moms get confused about all the numbers related to their babies.
That’s fine. You could also say “confused with” to indicate not only the bare fact, but also a bit of attribution of cause (the sheer number of numbers). It’s a subtle shift that makes it seem like just about anyone would find this many numbers confusing.
Most new moms get confused with all the numbers related to their babies.