To Be Dyed
intransitive verb, godan verb
If 染める is "to dye," then this is to be dyed. You aren't doing the dying, because you know that if you did it you would have done things right, unlike the other person who dyed your hair. This person marred (まる) it up really bad.
そまる
The reading is the same as 染める.
子供たちがこの悪い環境に染まってしまうことを心配してるのよ。
I’m worried that our kids will be tainted by this bad environment.