I knew that dc1 wasn’t developing typically by the time I was ttc dc2. I had concerns about dc1 by the time she was 7 months old (such was the severity of her behaviour and deviation from ‘typical’ development). Dc1 was diagnosed when dc2 was 6 weeks old, having been in the system for about 15 months by that time.
Dc1 and dc2 totally played together when they were small. They did (and do) understand each other’s needs - which isn’t to say that the toddler years weren’t fraught and very difficult at times!
By the time dc3 came along, dc1 had an EHCP, and had been in a fabulous SN school for 4 years. Dc2 was getting along ok in mainstream.
Both dc1 and dc2 played with dc3 nicely enough. Dc2 and dc3 are very close now - they are very similar in ASD profile, and in personality (which leads to clashes too). Dc1 is now in 6th form at the same fabulous SN school, and has come so far from the, frankly, isolated, withdrawn and difficult to engage toddler she was.
We have been incredibly fortunate (despite the extreme difficulties), and really are now in a good place. I am now a single mum, and to be blunt, a lot of the calm now is becaus exH is not here anymore. We manage days out, with a reasonable spread of things to enjoy - the hardest part there is finding something that a 15 year old and a preteen want to do, as well as being suitable for dc1 with learning difficulties, but we manage, just about. There is an enormous amount of planning, and an acceptance that our ‘normal’ and way of enjoying things is not necessarily the same as a lot of other families’, but it honestly is ok for us.
I am facing dc1’s transition to adult services with a large amount of trepidation, and of course I fear what the future holds. But there have been some very good times along the way, interspersed with the difficult bits (and a lot of the difficult bits have come from having to deal with admin and battling with local authorities etc, which really should not happen the way it does).