Wills, deeds, and other legal documents may list all the children of a specific individual. Don’t assume that they are listed in order from oldest to youngest. They may be–or they may not be. Try and use other records to estimate the years of birth for at least some of the children when vital records are not available. That may give you a better perspective on whether children are listed in birth order in a specific document or not.
Remember that a quit claim deed drawn up to settle the estate of a deceased individual may mention children and grandchildren of the deceased in order to transfer title properly. The deed may not distinguish between children and grandchildren, only referring to them as heirs. The deceased individual may have children who predeceased them and their children would be heirs. Some documents may not make all these relationships clear.
And obituaries? Well they can omit children, use a concept of “children” that is broader than biological children (for often understandable reasons), list children by where they live to save space, list them by gender, or simply list them in a random order.