Have you looked at www.kellymom.com?
She lists lots of references.http://www.kellymom.com/nutrition/so...ay-solids.html
WHO and AAP do not recommend a baby be fed solids b/w 4-6 months, although I'm sure this is what a lot of people hear. They say DON'T START solids before 4-6 months. AAP recommends exclusive BF for the first 6 months.
I think that if exclusively nursing a 9 mo old is DSS's only complaint, you're on pretty safe ground. Once a report is made, they have to investigate it. If it helps any, DSS is usually very suspicious of complaints in shared custody cases. Used to do this work in another country and often times the complaints were just differences of opinions and can not be considered neglect as defined by the government. Even if your DSS caseworker is totally ignorant about exclusive nursing, her superiors hopefully have more sense and if not, the medical professionals involved should be able to reassure them how healthy your baby is.
Surely the DSS caseworker can just talk to the ped, the IBCLC and the Dr. you saw and they can back you up? Can you do this in a way where you're not giving DSS a blanket permission to see all your medical records? I don't like those medical release forms that aren't very specific. They only need the info related to the BF and baby's weight gain. If I was that DSS caseworker and I was reassured by all those med professionals, I'd be closing the investigation pronto. Sorry to say it, but it's easier to cover your ass, if you have medical professionals telling you the baby is healthy and you can write than in the case file.
BTW my dd was exclusively nursed til 6 1/2 months and then I went really SLOW with solids. dd has always been small - the most she ever was was in the 25% for weight. Between 6-9 months she went down to about the 5th percentile for weight. My ped (who BF all her kids) wasn't too worried, said BF babies often transition to their genetic weight curve earlier than formula fed babies. I was concerned though because she never nursed much, just doesn't have a big appetite. Plus we have so many allergies on both sides of our family, I wanted to go real slow with solids and didn't want to introduce wheat or citrus til 12 mo. Anyway I started upping her solids at 9 months because I found she'd eat them for novelty's sake. She was really distractible and it was hard to get her to nurse enough. So there's nothing wrong with exclusive nursing and the BM is by far the best food at these ages, but I found if baby doesn't avail herself of enough of it, she'll lose weight.
Also starting solids really aggravated my dd's constipation. And rice cereal is the worst. That DSS worker is totally wrong about not feeding solids causing an anal fissure. Quite the opposite. DSS workers don't learn anything about nutrition either! Grains are actually more difficult than fruit & veges to digest at this age. dd's ped actually recommended we stop the grains. Dr's tend to push cereals because they're iron fortified. I found other iron sources like blackstrap molasses, added ground lentils to dd's millet porridge etc. I found even dd's ped looked at me a bit strange when I told her this - they don't learn much about nutrition in med school. And dd's iron levels at 12 mo were fine. An anal fissure is no small matter either - my dd had to be on milk of magnesia for months afterwards. I felt so bad for her, she was in pain every time she pooped I really sympathise with you having to deal with your ex and those in laws. It must be heart breaking.