Short Answer: You HAVE to have at least an APPROXIMATE 'Date', for each child.
There is NO alternative.
Such APPROXIMATE 'Date', can even just be an "About" 'Year'.
Even a 'guesstimation,' would be better than nothing - just note that such is a 'guesstimation' - just to ORDER the Children - in a "Reason Statement" .
You possibly have an idea of the approximate 'Year' of "Birth".
Even, if that is WRONG, you can change that later, when the actual "Detail" is known.
At least, something is better than nothing ...
The ONLY problem/issue that occurs is with "Multiple" Births - there is NO way to actually ORDER the "Multiple" Births if they were Born on the SAME 'Day', regardless if you actual include the 'Time' of 'Day' of the "Birth", for each.
Here are a couple of "Knowledge Articles" in 'FamilySearch':
Why are my ancestor's siblings listed out of order?
I do not know the exact date to put in Family Tree
I hope this helps.
what decades more or less did the family live?
as Brett points out - you can estimate years
if for example this family was on the 1940 census - you could use their ages recorded on the census to estimate years and then the system would sort them correctly.
the system will only sort by the years entered - so you have to enter something.
children will appear alphabetically until dates or approximate dates are listed.