Actually Goldsworthy say that the amount of sacrificed babies increased pretty much every year until 146 BC.

I'll try to find where he got that info from.
First, let's qoute that particular passage from Goldsworthy's The Fall Of Carthage, also known as The Punic Wars (I have both versions):

"In at least one aspect of religious practice the Carthaginians were more conservative than the people of Tyre. They continued the ghastly Moloch sacrifices of infants which were killed and burned in honour of Ba'al Hammon and his consort Tanit, a practice which had been abandoned at Tyre by the time Carthage was established.
The Tophet of Salammbô, the cult site where this ritual occured, is the oldest structure yet discovered by archaeology at Carthage and the excavations have shown that the practice continued until 146 BC. Disturbingly, the proportion of sacrifices where a lamb or other animal was substituted for the child decreased rather than increased over the centuries.
Similar tophets have been discovered at other Carthaginian foundations, but rarely if ever on sites founded directly by the Phoenicians. Religion was closely controlled by the state at Carthage and its senior magistrates combined a political and religious function."

In the back of the book it is stated he gathered this information from:

"Sacrifice to Melquart, Polybius 31. 12; religion and culture, Picard & Picard (1987), pp. 35-50, Lancel (1995), pp. 193-256, esp. 245-56."