Adopting for a second time...

[LegalNim]

My OH and I have a son who is ours by birth, however, I was very unwell during the pregnancy and hospitalised for the most part. We always wanted four children but cannot go through another pregnancy especially as I would be too unwell to look after our son at all or to work and my OH can't do everything on his own without it impacting negatively on our son. We understood that we would need to adopt our future children. We really want to adopt from as young as possible as we remember how precious those moments were with our son and so think that fostering to adopt is the route we'd like to go down. My parents were both foster carers when I was growing up (and both spent time in the care system themselves) and my dad was a care home manager/social worker so I understand the system pretty well.
However, looking at different agencies and preparing to start the adoption process, I've found places stating that you can't adopt twice unless there's an age gap of at least 12 years between the first adopted child and the second adopted child. Forgive me, but doesn't that just seem completely insane?!? Supposedly this is so children feel valued and settled before another child is introduced but I've just spent hours looking at studies into child development, psychology, social interaction etc and can only find evidence to support the opposite (that children who grow up with siblings and have siblings close in age are more well adjusted socially etc - not to say only children suffer or that age gaps are bad or anything like that though!). Surely this has to be a mistake?! Has anyone adopted twice and can give some advice here. Is this just a ploy to manipulate people into adopting sibling groups (not really an option for us for many years because they wouldn't place us with a sibling group with an age too similar to our biological son).
Essentially, does anyone know if you can adopt two children on separate occasions with a "normal" age gap in between the adoptions?

That does sound like a mistake. We've adopted twice and have 4 years between our girls. There are others on here with smaller gaps. For our LA you need to have at least a 3 year gap, but some have 2 years as the minimum. What you've been told sounds very odd.

Is 12 years a typo? Normally the expectation is a gap of 2 years.

There’s too years between my birth child and adopted child. Sibling groups weren’t an option either due to birth child being the odd one out. I also wanted 4 children but at this time, I couldn’t adopt another due to my sons struggle.

I suspect maybe the typo was that it should have read 12 months! Though most local authorities say 2 years I think. It might be worth thinking about how you would feel if you couldn't have the 4 you wanted. We always wanted 3 but it wasn't the right thing for my adopted son to have a sibling, he would have really struggled to share my attention so he is an only. We, ve made our peace with that now but it is a loss for us and him in many ways.

Thank you all for your responses. I'm hoping it's a typo but probably won't be going with that agency regardless. It goes on to say that anyone in their late 30s who is adopting should adopt multiple children at the same time (if they want to have more than one child) because they will be too old to adopt by the time they apply again. I'm hoping for around a 2 year age gap. We would ideally want four in total. I grew up with four within a nine year span and my husband had three within a nine year span. There was just over a year between my closest brother and me, and two years between my husband and his closest sister. We really enjoyed the closeness and have familiarity with that.
I'm sure we'll become more flexible as the journey goes on and we realise the pros and cons and see how our children are growing/developing/interacting but it's scary when you have a plan for your life and see a website that seems to shatter it.