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When you find a child's baptism, write down the sponsors ! ! Also write down all other records where the parents sponsor other people. And also their sibling's sponsors both ways. And even the sponsors of the sponsors ! !
You have to realize that most of the sponsors (or witnesses, or whatever you want to call them) were relatives. By putting the names of one generation in a circle, you often find a connected graph. Each person sponsoring their brothers, married sisters, and eventually their children. Many times, the older sponsors of the first couple children are the grandparents, but not always. Expect this analysis to take a long time ! !
OK, now that I said how great they are, here's the flip side. When a person moved into a new area, they didn't have any relatives nearby, so all their sponsors were just friends their age, local leaders, senior folks in the area, childless folks, church elders, etc. This is obvious, but be aware of it.
The other trap would be two brothers that marry two sisters. This happened, and your sponsorship circles will go around to the wrong families (you'll keep seeing the wife's sisters at both families' baptisms and think they're sisters of the brothers. Follow that ? ? )
I found that the most significant sponsors are the earliest. The couple chose their immediate relatives (and probably close, well-liked relatives) first on the list of sponsors, then with more children, started picking friends and prominent folks. That's my observation.
Here's a trick that sometimes helps with old church records. Sometimes only the man's name is given (eg, Jacob Conrad and wf). But since they often named the child after a sponsor, check the child's name. If it's a girl, often (not always) that is the same name as the sponsor's wife. You may have to hunt around for several records from the same time frame to predict a wife's name.
I've also found that cousins show up as sponsors. Hey, they fall into the friend classification above and didn't realize (or care) that it would confuse the genealogists later ! !