Well, how did they install the pipe? Maybe that’s your clue as to how to get down there.
Anyone call the fire department?
they aren’t trapped are they? would a bbq pit work?
Not trying to be flippant here, but could a midget fit in there? If a small child could, perhaps a little person could save the day. Seriously.
I believe they prefer to be called Little Peepholes.
Any updates on this? Did it rain last night? Were the puppies rescued?
Just got up, and no, no updates on my end yet but I have to say some of these suggestions are great. 
I’m only talking to her via text so I’ll have to wait until I hear from her. I’m going to send her a link to this thread.
No, it did not rain last night and now isn’t supposed to rain at all today now, so there is more time.
I’m not sure how it was installed, but I would guess it was laid down years ago and backfilled. It looks very old.
No, I don’t know where the mother is. I’ll pass on the suggestion of using another female to lure them out, thanks!
I don’t think they could get a backhoe in there, it’s pretty heavily forested. I think there might also be a worry of collapse or driving the puppies further in because of the noise. If they can get enough people to help hand dig, I think that’s the best option. But yeah, the ground around here is difficult!
George Carlin:
“ever seen a Pigmy rapist?”
(holds hand near waist level): " just little fuckers, about this tall"
Well, if you need more hands digging, just let us know - Jim and I have shovels, and we know how to use them. 
How about an electrician’s fish tape? They’re designed to travel around pipe elbows, so a culvert would be no problem. Feed it in while spooling out some poly rope rigged with a noose and lightly taped to the end. Snag a pup and pull it back with the poly. Pull back the fish tape and do it again.
Just curious - if the culvert is so small, curving and presumably dark, how did anyone find the pups in the first place?
I concur- make a long flexible pole out of two lengths of 1/2 inch plastic electrical conduit. Run a stiff nylon rope through it to form a stiff lasso at the far end. (a piece of 1/4 inch copper line can be used to push it through the pipe, one segment at a time, before you join them.) Use knots to limit the minimum size of the loop so you don’t frustratingly pull it through.
Using a powerful flashlight, a spotter’s scope if necessary, or even a plumber’s crawling inspection cam, lasso the pups one at a time and gently pull them out.
Its rare to have a culvert so small that an average not fat and not big person could not fit in it if they tried (and were not claustrophobic). Now, I have seen where you couldn’t get in the ENTRANCE, but that is different than not fitting once you are in there.
Have you tried figuring out where this culvert leads to? Figure out where the other end drains out and send somebody up from that end to get to the pups.
Ok, I have a couple of pictures I was able to upload to give perspective:
The opening is about 1.5 to two feet.
Here’s what you need to do.
Go actually measure that opening with a tape measure. If it isn’t round, get good measurements of all the dimensions. And up close pics of the entrance. Get a rough idea of how many feet it is from there to where the puppies are. Pace it off and measure how many feet one of your paces is and do the math.
Now, do an internet search for the National Speleological Society (NSS). I believe their website is caves.org.
They have a forum. Register there. Its free and you will probably be approved right away. If not email one the webmasters and tell them about your problem and the urgency. Make sure your title is something like Trapped puppies, Dayton, Need help Now! so it get immediate attention. Maybe even ask the webmaster to get this sent out to the cave rescue hotline/email thingy.
You are lucky as this is the weekend.
If that thing is big enough for a caver to fit a caver will probably be there faster can you can blink. They just need to know the actual size. You be amazed at how small stuff some cavers can fit in. They even have contests about it.
A fish tape will be much too flexible - you can push it through a 1" conduit no problem, but in 18" it will buckle and coil. But there are flexible fibreglass poles made for similar purposes that will easily reach 15’ into that sort of space. Any electrical supplier will have a set.
Definitely call a plumber. They’d be the most likely to have ideas and/or equipment that could get in there. Good luck. I hope they can get out safely. Poor little things.
Just a quick update on the lack of an update. She just posted on Facebook that they had to put their family dog down today. He’d been having problems breathing and this morning he stopped breathing twice and was turning purpleish, so they had to take him to be put down. She’s pretty devastated, and that’s obviously taken up most of her day. I have passed on a link to this thread though, and hope they’re able to take your advice and rescue those puppies.
Is this organization in Canada as well? We’re in Alberta (Calgary area).
Ooops.
Sorry, missed that detail about Alberta. Obviously the NSS is America based but somebody there will have Canadian contacts. And if its an emergency the information will get spread far and wide post haste if you ask them to do so.
But still do it. The earlier this evening the better. Seriously. The caver grapevine will spring into action and if that pipe is big enough for a human to fit and there is a Canadian caver within driving distance they will probably help.
Just give as many details as you can. And again, they will need to know pretty accurately how big that pipe is. There is a difference between fitting and not fitting and for cavers the difference can be just a few inches.
Cavers be crazy but they good folks.