A lot of times, when they're young, all you have to do is offer them a nice warm, thawed pinky on forceps. Just move it around, bump their tail with it, etc. to elicit a strike, and they'll usually will take it. I've switched all kinds of neonates over to f/t like that. Don't let it psych you out...it's really not that difficult. 
As for prey size, just about any Carpet hatchling can and will take fuzzy mice for their first meal, so there's no need for pinkies. And yes, it is good to introduce rats as a food item, while the animal is still young. Believe it or not, your JCP should be able to take rat pinks after another 4-6 meals. Don't be shy...offer it some big meals. Carpets can take some huge meals. A lot of times, I'll give them rats that are twice their girth, and they take them and digest them no sweat.
>>Hi. I have a new JCP that is feeding on live pinkys. He has only had 3-4 meals so far only one of which has been with me (a live pinky) I want to switch him to F/T and am asking for tips on how to go about doing this. What techniques have been successful for you guys? Also, should I try to get him onto F/T rat pinkys or fuzzies ASAP so he can acquire the taste and hopefully make a smooth transition? Thanks in advance. Jake
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Anthony Caponetto
http://reptiles.drivennewmedia.com