My children will attend CCD, however they also attend a non-denominational Christian school founded by Episcopalians. They attend chapel service as a school on Thursdays. There is also a communion day. I see nothing wrong with attending a chapel service, but what about the communion? Should I hold them out of this all together, or have them cross their arms as we require non-Catholics during our Mass?
It is gravely problematic for your Catholic children, who are not yet fully formed in their own faith, to be attending non-Catholic Christian services on a weekly basis – especially since you will not be present and may have no way of knowing what they will be taught at the services. If your children are required to attend these services and cannot be excused for reasons of religious objection, then I can only recommend that you seriously reconsider their enrollment in this school.
To answer your other questions, Catholics cannot receive Protestant communion. Non-Catholics are not “required” to enter the Communion line at a Catholic Mass with their arms crossed. They may do so if blessings are offered those not receiving Communion and they want a blessing, but they can also remain in their seats without participating – which is exactly what an adult Catholic should do when he or she occasionally attends a Protestant communion service as a guest. (Catholic children should not be attending a non-Catholic service at all, unless there is sufficient reason and they are accompanied by a parent or guardian.)