DD didn't sleep through until she was 4yo. At which point DS1 was born just a month after she started sleeping through.
DS1 didn't sleep through until he was at FT school either.
DS2 has always slept relatively well, but NEVER has more than 8 hours. If I put him to bed at 8pm, he is awake for the day at 4am. If I put him to bed at 9pm (his usual bedtime now), he is awake at 5am. Without fail. The only saving grace there is that he is now 9yo and can read a fucking book until a more reasonable time.
They have all got dxd hyperactivity.
I am having to do DS2's inhalers every THREE hours, day and night right now, as he has croup that's worsened his chronic asthma ATM. Normally it's every four hours.
And DS3 has roughly 6 hours sleep in every 24 hours, 4 at night and two in the day, but the two in the day are an hour nap in the morning and an hour nap in the early afternoon.
And I am finding it impossible to stop him napping as it's usually when I'm doing the school runs.
I have been permanently sleep deprived without a break for nearly 15 fucking years. My body is giving up now!!