Finding some families is challenging - due to transcription errors from hard to read documents. One thing I've learned, if not getting results 1850 forward is to search for one of the children's names and then discover that the fathers name was illegible and transcribed so off that the search couldn't match them. Also, to not enter specific dates - like if I know they were born in 1823, will ask for 1820 to 1826 or even 1815 - 1830. Dates on census records can be off by several years.