Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Muslim scholars have different opinions concerning the matter of letting non-Muslims enter mosques. The preponderant opinion is that it is allowed if there is any considerable benefit in that such as calling them to Islam. The evidence is the Hadith stating that Thumama Bin Athal was made prisoner in the mosque while he was still a Kafir and that was during the era of the Prophet (sallallaahu alayi wa sallam).
Allah knows best.