Although Moshe takes his wife and child(ren - see Ramban) along when he departs Midyan to go back to Mitzrayim, it is not clear that they actually completed the journey with him. "Vashav artzah Mitzrayim" (4:20) -- HE returned -- singular, implying Moshe alone came back. We know from Parshas Yisro that Moshe's family rejoined him at that point in time, meaning that at some point they separated. Ibn Ezra writes that Moshe sent his family back after stopping at the inn to mal his son. Ramban suggests that Moshe's family might have came back to Mitzrayim, but Moshe may have sent them back to Midyan because Tziporah missed her father.
Ramban quotes a Midrash: Yisro asked Moshe where he is bringing his wife and kids. Moshe replied that he is taking them back to Mitzrayim. Yisro then asked: the people stuck in Mitzrayim want to get out -- why would you bring your wife and kids into such place!? Moshe answered: eventually those enslaved will be freed and come to Har Sinai to hear "Anochi Hashem Elokecha asher hotzeisicha mei'Eretz Mitzrayim," I am G-d who took you out of Egypt. If my sons don't go back, they will not be privileged to hear those words. After hearing that answer, Yisro consented for them to leave.
Why did Moshe think that if he doesn't take his family back to Mitzrayim they would not hear "Anochi Hashem Elokecha...?" According to some views Yisro and Moshe's family rejoined him post-yetzi'as Mitzrayim before mattan Torah. Not being in Egypt did not preclude them being present at mattan Torah. Even according to the view that Yisro and Moshe's family rejoined him later, there seems to be no logical or logistical reason they could not have come earlier to be present at mattan Torah. Why did Moshe think that it was impossible?
I think what Chazal are telling us is that the same words "Anochi Hashem Elokecha asher hotzeisicha..." carried a far deeper more significant meaning for the person who had been enslaved in Egypt and was redeemed by G-d than they did for the person who had not been there. Moshe was telling Yisro that if his children do not taste the bitterness of exile and experience the joy of redemption, they will miss that depth. Yes, they might be there to hear the words, but those words will not mean the same thing to them.
When we hear words of Torah, it's not just a text. It's a description of our shared experience, and it's that shared experience that gives it context and meaning.