they look to be between 2 1/2-3 weeks, and look a bit on the dehydrated side, or at the least, underweight.
with hoppers, i'd give them oatmeal soaked in KMR (kitten milk replacer).
what type of mouse food do you use for your pet mouse? is it a pelleted food, or is it a seed mixture? if its a pelleted food, try soaking some of it in warm water. it should soften and be easy for them to eat.
when i kept mice, i normally fed them a mixture of dried pasta, oatmeal, dried fruit, cheerios, total, and high quality dog food. adults would get fresh fruits and veggies daily, as well, but you have to be careful when they're that young. the dried mixture got scattered throughout the cage, not served in a bowl. this gave them some of the stimulation they needed, essentially searching for their food.
now, i know nobody else has mentioned it, so i will. wild mice can carry all sorts of nasty diseases. i would never try keeping them because its not worth it to me to get sick. at the very least, i would not handle them with bare hands, or really at all. if i found baby wild mice and wanted to take care of them, i would keep my contact with them minimal- just provide fresh food and water, then release them back outside at 4 weeks.
even if you decide to keep them as pets, and work with them regularly, you will likely always have a pair of jumpy, wild mice. it takes several generations to domesticate them. they will also likely chew like crazy, so you'll need to be extra careful to provide them with safe things to chew on, and make sure their water bottle and the cage itself is chew proof.
good luck!