My wife converted to the Catholic faith. She grew up a Baptist. She involves our children in the summer vacation Bible school at her childhood Baptist church. I need a sound answer for why my child, who recently received First Communion, cannot participate in communion at the Baptist church.
Since your wife is a Catholic convert, I suggest drawing on your shared beliefs and pointing out to her that the Baptist communion is not Jesus. Catholics can only receive a valid Communion, confected by a validly ordained priest, because only that Communion is really and truly Jesus Christ, body, blood, soul, and divinity. Your child could be taught to pray silently during communion time (such as “Dear Jesus, please be with me now”), but should be taught to politely decline participation in the Baptist communion (“No, thank you”).