yes a mistake was made, but time will tell how good/bad the situation is. I think you are being a good mom by helping out and trying to readjust for all involved.
the mom I help out, she was 16 when she had her little one–the same age as my niece when she had her 1st. They are different like night and day. M is working, trying to educate herself and make a better life for their little family. baby girl was just over 2y when M asked for help–with no mother figure other than the daddy’s mom, she felt she needed guidance from someone she trusted.
My niece has 6 kids–3 different fathers, on her 2nd marriage and lives in the basement of her mom’s house with 9 other people. She has no motive to move on and move out. she is a 3rd generation teen mom and her oldest daughter is 4th generation. They just continue the cycle–little education, few job skills and no common sense.