A lot of thought has gone into the royals trying to get little Nickie. I would ask, why?. Diana was part royal, with real powers now. Nickie is a half hex/half grimm, he may never have powers(lots of Nick's family, Josh did not). If a male he might get powers in a few decades. He might be put on a watch list, to be checked every so often. If the royals try to hurt/kidnap Nicke, two parents would be out for blood. Members of both the hex and grimm clans might take an interest in this, since their own children would potentially be at risk. Why would the royals cause trouble for themselves, especially since it might never be an issue, and if so, not for a long time?