The chin has to feel comfortable with being picked up other wise they will likely freak out some. All 5 of my chins don't really care to be picked up at all. They will bolt away if they think you are trying to pick them up. I even have one chin that does not like being pet on the back half of his body, because he associates that with being picked up.
On the other hand some chins do well with it. From what iv heard its generally easier to start that process at a younger age. But no matter what the age it will take time. And its something you shouldn't rush. It can also be personal. If you succeed in eventually having them let you pick them up, they may still not let anyone else try.
Some basic methods involve letting the chin get used to you and your presence first. (as with any chin) Then trying various things like putting you hand into the cage, and letting them come to you. They might nose you or nibble, or hop up. Leave your hand their, let them do as they please (within reason). The idea is to let your chin become comfortable with you more, and comfortable being off the ground and in your hand (or arm if the crawl further up.) Eventually you can move towards picking them up bit by bit. But don't rush it. Each process can take time. How much depends on you and on the chin. Could be days, week, months. And of course, some chins just don't like being picked up.
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As for the comment of being able to pick them up like rats, i personally don't agree. Chins really arnt the type of animal you want just anyone coming in and picking them up at will.
Not only could that stress them out which is bad for them, but if you don't no what your doing or not used to it, you could hurt the chin. Any time mine are picked up, they squirm like crazy and try to get away. But they are fragile animals, and there fur is very smooth, it can be hard to get a grip sometimes. And if your not used to or expecting that, you end up doing something that would hurt them (like suddenly squeezing to hard while trying to get a grip). Or they could escape your grasp and go running off.