Mine are older, ds1 (8) has AS, ds2 (6) is NT as is their 2 year old sister.
We used to be able to take ds1 anywhere as he was pretty compliant, but as he's got older its become more difficult. Partly because he is no longer compliant and has a default setting to want the polar opposite of everyone else in the family
and partly because when we do go out he is bigger (obviously) so people's perception of him has changed so we have to be more vigilant of his behaviour, some of it would have been ignored by others when he was a toddler.
We went for a lovely Sunday stroll along the tow path the week before last - NEVER AGAIN! We had all three dcs, with dd in the offroad pushchair, plus two dogs and ds1 was the only one we struggled with. I spent the whole time steering him away from the edge before he fell in and trying in vain to get him to move out of the way of people that wanted to pass, with him blissfully unaware of their presence.
We are starting to find that ds2 is beginning to resent ds1 these days. Its a combination of things, firstly we reckon that ds1 takes up about 90% of our energy and resource and the other two end up sharing the 10% scraps and secondly, we are restricted in the places we can go, as if we go somewhere ds1 doesn't like or can't cope with, there will be an inevitable meltdown, which ruins the day anyway. eg We have never been to the cinema, because ds1 is phobic of them and last time we went to a VW show (which ds1 usually loves) he panicked because it was on a new site he hadn't been to before and we ended up eating a picnic in the carpark, then leaving.
Poor old ds2 jumps at the chance of going to the diy store with dh, just to get out somewhere. Last weekend when we said we needed to go out he piped up "I'll come" immediately, we said "but you don't know where we're going" and he said, "I don't care anywhere is fine, I just want to go out".
He is also ridiculously excited about his day off school tomorrow to go to the eye hospital, because it means a whole day with Mummy without ds1.
We are planning to do start planning days out individually and/or alternate weekends when they get to take turns in choosing where we go.
Is there someone who could babysit for ds once or twice a month so you can have a day out with just dd? That's our other option. Ds1 adores my Mum and likes her house because its calm and quiet, so sometimes he's happy to be dropped off there while we go out with ds2 and dd for an hour or so.