you can get some polygrip and see if you could put it on that way, but he might swallow the crown if it came loose again. if you put it in, you would want to use a temporary cement. that is, if you still have it. it really needs to have permanent cement from the dentist. is this a baby tooth? if so, i wouldn't worry as much, since he will get a new tooth later, anyway.
if you don't have it, you can go to the dentist and get a temporary crown. we have that last up to a year, made by the lab, that are $60 ea. but, other dentists probably charge a lot more. still, it should be a lot cheaper than getting a permanent crown. we have others that we make at our office that are even cheaper, but those are designed to last a month or two.