Your child is too small for you or your wife to go in for a permanent method
of sterilization. Deaths due to accidents do occur up to age of 5 years. Also, sometimes infections like diarrhoea and chest infection can take a serious turn in these little children. I would advise your wife to use the IUCD (intrauterine contraceptive device) or take an Injectable contraceptive (every 2 months/3 months, depending upon the injection). The injectable contraceptives uwould be just fine, except that she will tend to have no periods, and every 2/3 months she MUST take the injection.
Theoretically, there is a way of storing your semen, should you decide to ndergo vasectomy. In case of an unexpected death of your child the sperms from your frozen semen can be used for fertilizing the egg of your wife-IVF-ET (test tube baby). But these are very expensive procedures, available only in a few centers, with success rates of ~ 30% in the best centers in the world. After a conventional vasectomy you need to rest for 5 days (max), but you or your wife should use a contraceptive for 4 months after surgery as sperms are seen in semen till 4 months. After a no-scalpel vasectomy, you need to rest for 1 or 2 days only, but still have to take precautions for 4 months after that.