Max and William Hoad uncovered the loot while walking along the riverbank in Usk with dad Simon.
They spotted a brown bag beneath a bush, hidden under leaves.
Six-year-old Max said: "I saw a glimmer of silver and knew it was going to be treasure."
The 'treasure' was actually three silver chalices and two silver collection plates.
They handed the find into Usk Police Station and after some investigation, it was discovered that the silverware had been stolen from St Mary's Church in Monmouth back in 2010.
William, aged eight, said: "I was really pleased we had found the stolen silver but I was scared in case we rubbed off the fingerprints of the thief and got our fingerprints on them instead."
Not all items stolen from the church were among those found on the river bank but the junior detectives are keen to continue their good work.
William added: "We want to find the rest of the silverware but we think it might be a bit further away now. We're going to keep looking to see if we can find it."
When asked if they wanted to become detectives when they're older, Max said he would like to be a detective but William wants to be an archaeologist.
Inspector Geoff Smith presented the two children with a certificate and also some silver coins... of the chocolate variety.
He said: "We're really impressed that the children found the silverware and know that the local community in Monmouth and members of the parish of St Mary's will be very grateful that the chalices and collection plates were found and returned to them."

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