Ver, I do live in an extremely poor country.
You have two things to consider. One is the likelihood of getting the disease in question, like typhoid. The other is the possibility of getting high-quality treatment in time.
It really depends on where you are going.
Let's take the likelihood of getting a disease. For example, if you are going to South America, polio is not going to be an issue. Even in most of Africa, your statistics for getting polio are nearly the same as in the United States, i.e. zero cases per 100,000 or whatever. If you are going to Gujarat in India, that's a different story.
Tetanus is not going to be more likely anywhere, provided your kids are well-supervised and are not playing in areas where they can get lots of scratches.
The typhoid vaccine is for fives and up anyway.
In most poor countries, you cannot guarantee that your children are going to be drinking only clean water, because they may drink water at their friends' houses, for example, where it's not boiled properly. Or they might ingest water when swimming. Or they might drop food on the ground and pick it up to eat it before you see them doing it. Or whatever. Many very attentive parents in poor countries suffer because most of the population is too poor and uneducated to take the proper precautions, and this makes all people more vulnerable. So this raises your risk for everything, including diseases that cannot be prevented by vaccines (like giardia). The poorer and worse off the country, the higher your risk, just because of environmental contamination.
Now, on to treatment. In South America especially, and in a number of North African countries, they have some top-notch hospitals where you can trust what they are giving you. You do not have to constantly ask yourself, "Is my child getting expired antibiotics?" or "Does this doctor even know what tetanus is?" or "When will we get to the hospital? It's been four hours in the ambulance already!!!" So, for example, if you forgo tetanus, even though your chances are not as good as in the U.S. or, say, France, you still have a good chance of getting your kid life-saving treatment.
On the other hand, where I live, most of the good doctors have emigrated and most of the drugs we get are dumped on us when they expire. They overprescribe antibiotics, the hospitals often have the water turned off because the government doesn't keep the well pumps on, and sometimes the doctors have literally bought their diplomas a week ago. It is a very sad situation. So here, if my daughter did get tetanus, or pertussis, or the measles and got complications, we'd be screwed. It would actually be quicker and more effective to leave the country, and that is not saying much since flights abroad are not even daily.
Incidentally, I wouldn't go for the OPV for your own sake. It's mainly for the protection of others, so that you can't spread the virus to them. Though, it's much nicer (you swallow it instead of getting a shot). Anyway I just wanted to say, you don't need to get the OPV if you don't want. If you are just trying to keep your own kids safe, either the OPV or the IPV will do.
I would suggest you look at where you want to go, and then come back to this forum and Finding Your Tribe with more specific questions. Ultimately, though, it's still risk vs. benefit and you will need to decide for yourself. Good luck!