"Your child" is singular and "them" is plural. The most logical solution would be to use the singular form. The singular form of them is him or her.

A teacher friend brought me this mistake from the Saline Express. "Obove" should be "Above." Perhaps it marks a trend in our language to adjust words so as to make them more like the word "Obama." It's a language revolution!! Ha!

I circled 3 mistakes before I scanned this ad. First, "it's" does not need an apostrophe because the writer does not mean "it is" or "it has." Second, "slower" should be "more slowly." More slowly is the adverb form telling how it migrates. Migrates is a verb. Adverbs modify verbs. The third circled mistake, my favorite mistake in this ad, is the misuse of the word "lessons." This writer should have used "lessens."