For families that lived during a time of no vital records genealogists often do not have dates of birth. In some cases, it may even be difficult to estimate years of birth if records are not available. In cases such as these, make certain that you indicate the birth order is either a guess or inferred from the order of children in a will or another document. If children married, years of birth could be estimated from the marriage dates.
And ask yourself, would any of my conclusions change if the order of birth for these children change? Most times they wouldn't, but you never know.