For me... it got better once my kids hit 2-3 years old.
Then they slept more soundly.... and longer and better.
But... my kids are both very loud when they sleep.... talking in their sleep or if they have dreams.... they laugh, grumble, or cry if having a nightmare.
They do go back to sleep on their own... or are just still sleeping when they are doing this.
At about 2 years old, it gets better.
But if you can't fall back asleep.... well, I don't know. My Husband is like that... with any little noise.
Its just the way it is. Kids or not.
Even my tossing or turning or snoring... will wake him.
So its not always the "kids" that are waking a parent.
If you have another baby... well, the 2 other kids will be older by then... so they will be sleeping better naturally, amidst their age-related sleep tweaks. Then with a baby, you will not get sleep. Again.
For me personally, I never get 8 hours of sleep. I have my own sleep rhythms... I get about 6 hours sleep.
all the best,
Susan