Life is life. I have a cat that is great mouser and I get occasional gifts. My dogs will find rabbit nests in yard and I would see nest destroyed.

What can yo do?

If mom doesn't come back, the babies are pretty much dead, since they cannot see, move well, or eat beyond mother's milk. There are definitely more babies if there was one. I would expect like half a dozen or so.

Since it's been a couple days since your surprise discovery, a few situations are possible:

1. Mother mouse came back and moved back in ... there are mice in there, and they are alive, mother might jump at you again. You'll have to decidewhether you want to leave her and buy new dirt or evict.
2. Mother mouse came back and moved the nest ... there are no mice in there. Just use the dirt.
3. Mother mouse did not come back ... there are no live mice in there; the babies would have died without their mother. Just use the dirt.

Please be aware that mouse poop can be dangerous (toxic, cause illness, etc.), so please take caution when working with things that have been in significant contact with them (like this nest) or when cleaning up their leavings.

callirhoe, I agree that it is difficult to make a shed mouse proof. But my husband tries just about everything! I think I'm the one who leaves the door open for way too long, especially early evening, before dark. Unfortunately the babies are not mobile yet. Must have been born just days ago. Maybe I'll move the bag when the babies have grown and are able to run.

lindalana, I know what you mean. Only thing now is that I feel responsible for their lives! When they are gone, then it will be out of my control.

BlueberryBundtcake---very thoughtful response! I have to believe that the mother came back because (1) the baby was not there anymore and was not mobile to move itself and (2) I have been leaving a tiny bit of food nearby and it is always gone! I wish it was your number 2 that was the reality! But if I leave the food, and it's gone, then I suspect the mother is there and all the babies! I'm not looking forward to cleaning up the media!

I'm afraid to look and find tons of babies. I'm also afraid that the mouse will jump out and scare me again. And maybe there are some dead babies? Oh dear!

what an unpleasant surprise 🙁..

Baby mice are basically little pink erasers for about a week, at which point they start to become furry lumps. It's close to two weeks before they open their eyes, move around much, or eat solid food (before that, they aren't capable). They're not weaned for another week or so after that.

If you are feeding the mouse, it's unlikely to leave ... you're more likely to attract more.

BlueberryBundtcake, no fur on what I saw, so the babies are then maybe a week old or so. Feed the mouse and I'll attract more? Yikes! I don't want that! Good point! I guess I thought if I leave food and it's gone, then I know the mouse is still there. So now I know it is still there. And if I don't give it some food, it may die and all the babies too? I don't want to find dead mice in my potting mix---or anywhere else for that matter!

I am going to get some new potting mix. I've looked at my choices and have decided I am just going to get some peat moss and add perlite to it (which I already have). Then I can just add the unused peat moss bag to my garden soil and not have another bag of stuff to store over the winter.

Bought some peat moss! Moving on with my garden potting!

The mouse survived before you started feeding it. Mice breed like crazy and don’t need any help from humans.* Note what was said above about mice being disease vectors.

*Obviously there are rare and endangered species but I’m pretty sure yours isn't one of them.

"It's difficult to mouse/critter proof a shed" HAHAHAHAH It's difficult to mouse proof a home--a shed CAN'T BE DONE! The bat man came to advise and he said they will not guarantee mouse proofing. They can get in in any gap as large as a pencil. You have disturbed the nest. I would lay the bag down cut it stem from stern walk away for a day then return and put the dirt in a large container with a lid. Plastic bins, metal barrels are mouse proof. Live and let live when dealing with nature as much as possible but you have already disturbed the nest and where animals are concerned one needs to let nature take its course.

I found a mouse nest with babies in it in our garage once and just picked up the whole nest and placed it in the shade outside of the garage. I didn't want to kill them but rather let nature take its course. They were gone the next morning so i put the nest in the woods to decompose.

arcy_gw, and I was worried about my compressed potting mix getting a few holes from the critters outside! I thought the bag was "safe" inside the shed. We used to get mice in the shed, but my husband kept working on mouse proofing it. Things were going along fine until now. I guess the mouse has found or made a hole big enough to get in. Laying the bag down outside, and leaving it sounds like a good idea. Not sure I can do it. I'll try.

Since one of my sons so kindly sent me a TikTok video of a family of snakes crawling out of an opened bag of potting soil (he knows I’m petrified of snakes 🤯), I will never ever store any potting soil NOT closed up inside one of those big plastic storage tubs with a lid. The potting soil dumped in, plastic bag tossed, and the lid securely closed.

Never ever ever leave a bag of potting soil just laying around.

Yesterday I asked my husband to move out the potting mix out of the shed and the plan was to lay it on its side (like you suggested arcy). He carefully moved it, but before laying the bag on its side, he looked inside. There was a clump of materials on one side, but no evidence of mice. I am wondering if when I had dug into the soil---the mouse moved out with the babies. Or are they further down in the bag? Or in another spot in my shed! Left the bag outside last night. Planning to move it back in the shed today.

Learned a lesson. Just as was suggested, plastic containers should be used to store potting soils or similar products!

Mice grow fast. The babies you saw are the equivalent of teenagers by now. In a couple of weeks they'll be starting families of their own.