A "Reformed homeschooling mama" recently asked: "how do you all deal with toilet humour in a 4 year old boy? He will have days where it’s all he seems to joke about and I feel as if I’m constantly telling him that kind of thing is not funny!!"
Because this touches on a part of our Eph 6:4/Deut 6:5–9 duty that I believe few think about, I took the time to republish my answer here. If Christians today would band together and heed God's Word on this, what a generation of mighty and wise speakers God might be pleased to produce from our children!
Col 4:6. Let your speech always be with grace, seasoned with salt, that you may know how you ought to answer each one.
Eccl 10:11–13. A serpent may bite when it is not charmed; the babbler is no different. The words of a wise man’s mouth are gracious, but the lips of a fool shall swallow him up; the words of his mouth begin with foolishness, and the end of his talk is raving madness.
Phil 4:8–9. Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy—meditate on these things. The things which you learned and received and heard and saw in me, these do, and the God of peace will be with you.
Eph 5:1–5. Therefore be imitators of God as dear children. And walk in love, as Christ also has loved us and given Himself for us, an offering and a sacrifice to God for a sweet-smelling aroma. But fornication and all uncleanness or covetousness, let it not even be named among you, as is fitting for saints; neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting, but rather giving of thanks. For this you know, that no fornicator, unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and God.
From their first beginning to speak, it's good to talk to them about the importance of words—how God set apart words as His own means of creating, and communicating Himself, and bringing us to faith, and sanctifying us; how He calls the Son the Word; how a big part of our being made in His image is using words; what a tremendous responsibility this is, then, to speak always that which is with grace like God does, edifying, helpful, glorifying.
Where it connects to your current situation is that "toilet" stuff is something that we still share with the beasts. God made us out of the dirt, that we might be ever humble before Him. And especially that we might marvel that God the Son became like we are, subjecting Himself to have one of these dirt-origin bodies, and even to have to use the toilet—though the Bible never speaks about when He did so, which is a good clue to us that this is not one of those kinds of speaking that builds up and gives grace. But the Lord Jesus humbled Himself! And the fact that we have to use the toilet humbles us too.
So this is something that you mitigate on a continual basis, positively emphasizing the right and noble use of all of our speech.
The reason his potty talk grates upon you is that believers intuitively know this, but sometimes can't quite put our fingers on it. If you are primarily engaging at the point of potty talk, then there will be a big gap missing in the foundation of helping him use his speech well on the whole. You may even find yourself provoking his fleshliness by emphasizing what he cannot do, rather than appealing to something that you are praying that the Spirit is producing in his heart: a recognition of and desire to please a heavenly Father Who has adopted him, a Redeemer Who has purchased him, and a Spirit Who has indwelt him.
Of course, if we are going to teach our children to use words this carefully and intentionally in the love and service of God, then we ourselves will need to be aiming at the same and practicing the same. The Lord help us to do so!