Once you've figured out that your ancestors married at a reasonable age [say, 18-30], you can sort out the children.
 Although there may be a few close calls, the eldest child should be born a year or two after the parents married. [Parents marry in July 1765; 1st child born February 1766. Possible under certain circumstances, like the bundling bag failed to hold.
 After the 1st born, couples generally had a child every 18 months to 2 years. If there are large gaps between births, a few possibilities exist: [a] infant(s) died young, stillborn, miscarried, etc.; [b] you haven't found all of the kids yet; [c] some event prevented the couple from having children, like a war.
 Most women, before the past few decades, stopped giving birth around 40. This was primarily for health reasons. If children are being born after the mother reaches 45, it is probably a red flag. After 50? Whoa!
 Large families were commonplace before the 20th century. Most families were still living on farms and help was needed. The odds of all of the kids reaching adulthood was slim, but did happen frequently. A family with 6-12 children was not uncommon. Now if you come across a family with 21 children with repetitive names [3 Johns, 2 Marys, 2 Sarahs, 2 Williams, etc.] and repetitive birth years, chances are 2-3 tree have been combined. Sort with care and common sense.
 In determining if kids fit, look at the mothers age at marriage [say 20] and count the years to 40 [again 20]. That allows for about 10 kids [1 every two years], give or take - allow for multiple births, miscarriages or mom having 1-2 babies after 40.