Cardinal Newman said “To be deep in history is to cease to be Protestant.”
In addition to Keatings “Catholicism and Fundamentalism” I would recommend a couple of other books-
“Faith of the Early Fathers” edited and translated by Jurgens- at a minimum Volume I.
'Surprised by Truth" collected and edited by Patrick Madrid. Conversion stories of protestant ministers.
You have two issues as I understand it:
First issue. Concern for your kids. Have them read the bible as well as the books that have been recommended. I find ‘Faith of the Early Fathers’ particularly helpful in countering protestant arguments that the Catholic church has strayed from the practices of the earliest Christians. (St. Justin the Martyr’s description of a mass in the year ~148 is something I read to my 7th grade CCD class. Other than not mentioning singing, it is exactly what we do today).
Since we as Catholics believe in scripture and Sacred Tradition, and most protestants emphasize Sola Scriptura- you need to address that with them. What is our and the protestants authority for accepting our respective versions of the Bible as scripture? We rely on the Church’s authority- what do protestants rely on in accepting their version of the Bible as scripture? Kids do need to know this, that there are differences (deutero canonical books). As well as the Catholic Church teaches the whole truth which consists of Sacred Tradition along with scripture. A couple of handy quotes for your kids to see this is in fact biblical in responding to protestant criticism.
. 2 Thessalonians 13-17
13 But we must always thank God for you, brothers whom the Lord loves, because God chose you from the beginning to be saved by the Spirit who makes us holy and by faith in the truth. 14 Through our gospel he called you to this so that you should claim as your own the glory of our Lord Jesus Christ.
15 Stand firm, then, brothers, and* keep the traditions that we taught you, whether by word of mouth or by letter. *
16 May our Lord Jesus Christ himself, and God our Father who has given us his love and, through his grace, such ceaseless encouragement and such sure hope,
17 encourage you and strengthen you in every good word and deed.
John ch.20
There were many other signs that Jesus worked in the sight of the disciples, but they are not recorded in this book. 31 These are recorded so that you may believe that Jesus is the Christ, the Son of God, and that believing this you may have life through his name.
Second issues- continuing apologetics work, which requires really knowing the scriptures. Particularly entire passages vice the snippets protestants tend to quote. Really hard work, I find it beyond my abilities at the moment.
I could go on about it, but Keatings and Madrids books are a very good start in common protestant criticisms and responding to them. In addition to the solid grounding the Faith of the Early Fathers will give you in understanding the early church.