It hasn’t changed though. Perhaps you’re mixing up US citizens vs permanent residents petitioning for spouses and step children. Permanent residents do not need separate petitions - the children would be derivatives under spouse’s petitions. This isn’t applicable to US citizens.
I would advise to read official instructions for I-130 and any other forms as well. They are very helpful and it would be neglectful to ignore them.
Under special instructions drop down section, on the USCIS website under I-130, it states the following:
You must submit a separate Form I-130 for each child if:
The relative you are applying for is your spouse;
Together you have biological children, stepchildren, or adopted children, and
You did not file separate petitions for them.
https://www.uscis.gov/i-130