" I have just installed DNSCrypt to protect my DNS queries, but I would also like to use something like proxpn.com or other (please suggest)."
With certain VPN services you can use OpenDNS or DNSCrypt also with the VPN.
You ask for suggestions:
"I have whitelisted proxpn.com. However OpenDNS is stlil blocking it, even after half an hour of waiting."
Sure, you need to flush both, your local resolver cache and your browser cache, after each such settings change. Else you'll be served out of your caches which can even last for weeks. Half an hour is nothing.
"I guess what I am trying to do is prevent internet snooping by my ISP/NSA"
If you trust remote VPN/Proxy services and servers you connect to more than your ISP, then be it.
Portions of paranoia are ingenious.
"but protect my four children from porn at the same time. What's the best way to accomplish this?"
You configure your network to use OpenDNS, and use a VPN proxy on the computer (or under the user account) you want to do this.
