Samuel, in the days of his childhood, appears to have ministered unto the Lord some time before he really knew Him. "Samuel did not yet know the LORD, neither was the word of the LORD yet revealed unto him" (1 Sam. 3:7). The Apostles themselves do not seem to have understood all that our Lord said at the time that it was spoken: "These things understood not His disciples at the first: but when Jesus was glorified, then remembered they that these things were written of Him" (John 12:16).
Parents, comfort your minds with these examples. Be not cast down because your children see not the full value of the means of grace now. Only train them up to a habit of regular attendance. Set it before their minds as a high, holy, and solemn duty, and believe me, the day will very likely come when they will bless you for your deed.
Taken from the book The Duties of Parents by JC Ryle 1816-1900