My dfs had this for two-three weeks (actually, maybe longer??) in his first month or so of life. It developed way before he had toenails long enough to trim. It doesn't have to do with being an attentive parent. I had his ped look at it. His ped said it is very common because baby toenails are so soft, they just grow right into the skin. Fortunately, because the toenails are so soft, ingrown toenails on babies almost always resolve on their own. The ped thought it would have to be pretty bad before he would interfere. My dfs's ingrown toenail was very swollen and red, but as I recall didn't seem to be terribly painful.
The ped said to just leave it alone. So we did. And after a while it was gone.
I'm pro-adoption reform, but not anti-adoption.