Two issues here. First, the general one about children having choice of religion - and I can only speak from a Christian (mainly Orthodox) perspective of course. A Christian believes that having been admitted into the Church pretty much guarantees passage to the "better place" provided you have not committed serious sins. In the case of children, who have had limited opportunities to sin yet, this means that in the case of accidental or otherwise early death, being "in the Church" is a guarantee of Heaven in itself (I am using the term "admitted into the Church" on purpose here - in fact for some dogmas like RC or Orthodoxy one has to be actually baptised, and thereafter tutored by your Godparents up to adulthood).

In centuries past, when child mortality was much higher, this "guarantee" was a major factor in parents choosing to indoctrinate their children - and have them baptised - early. The reasons have largely elapsed now of course, but the practice remains.

Of course, even I managed to loook cute at 8 months old being immersed into the fond and displayed starkers for all to see before being anointed with oil on all (ALL) my importants parts while bawling my heart out. The imagery of doing the same as a teenager or older doesn't bear thinking! (OK, you do have late converts of course, and they are dressed in a white robe while being immersed, but still...).

But the issue of the JWs dragging a kid along on their door-to-door canvassing is something else altogether. This is not part of the child's indoctrination or religious education; the child is there simply to impress the adults opening the door; it is a selling technique, and the child is being EXPLOITED. Pure and simple.