Well we can not really know but when he was a child he may have had pagan beliefs since pagans were the majority in the Arabian peninsula and because he was from Mecca. Mecca even before the rise of Islam was a place that pilgrims would journey to for the Ka'ba (hajj). The hajj to the Ka'ba was a pre-Islamic pagan tradition before it was an Islamic tradition but in Islamic doctrine the Ka'ba was built by Abraham so it technically isnt pagan. Pagans were the majority in the Arabian peninsula before the rise of Islam, but there were people of the book (Christians & Jews) in the Arabian peninsula at that time.

Before Muhammad was the prophet he was a merchant and led caravans to Syria for his future wife Khadija, the belief is that Muhammad made contact with Christian monks etc. and learned about the Abrahamic religions from them.

Most of the historical records that still exist about Muhammad that are not the Qu'ran appear 100-200 years after Muhammad's death and the best source other than the Qu'ran is probably Al-Waqidi. You wont find the answer you are looking for in the Qu'ran or from Al-Waqidi so your best bet of speculation of "maybe" is as close as you can get.

John L. Esposito has a lot of books on Islam if you want to find out more about Islam & pre-islamic Arabia.