Mice, and I believe rats, are at least as distant from their wild brethren as dogs and wolves........the time span in years that they've been domesticated may be much shorter...but you also have to remember that they reproduce exponentially faster than dogs and cats....mice and rats are normally...
If that size is acurate that sounds more like a mouse than a rat...a baby rat with its eyes open would be much larger. Either way you should provide a good rat food (oxbow or reggie rat are decent and easier to find than some others)....you could do Kaytee Forti-Diet (NOT the crunch, and NOT...