Thanks for everyone's tips so far. I probably got an hour of broken sleep if that after 3am before having to get up for the day. Of course DS is fast asleep.
Sleep training - I honestly don't think we need to do this. He has slept through for practically 2 years, we've had no sleep regressions and up until a week ago his sleep had been fantastic, we're talking 12-13 hours a night with no wakings. And over the last week it hasn't been every night, it's probably been 4 occasions in the last 10 nights. Looking back this morning I think last nights shenanigans was because he was hungry. He ate hardly any tea last night and my parents had mentioned when I got back that he should be hungry as he didn't eat much lunch. Can't believe this didn't click last night or during the early hours really! I think once I've sorted the eating out the sleep will settle as I bet if I looked back on what he'd eaten the day before the other awakenings I'd find the same.
SEN I don't think there could be an issue (or if there is it's minor) because the fact he doesn't seem that bad for my parents and the fact nursery haven't said anything indicates he's choosing to behave like this with me/DH/DD.
I agree about the high chair however he is quite small (still in 12-18 month clothes) and our chairs are too low for the table. I do have an Ikea toddler dining chair from DD which DS sits on however the seat is quite thin and because he seems to have no sense of danger I worry he will topple off as it's quite high off the ground. If anyone can recommend a toddler dining chair with arms on that won't cost the earth please let me know. I do have a play table and chairs he uses so I'm going to try and see if how he gets on eating meals off there.
I haven't read any books, with DD I felt like I was stepping into the unknown so I read books on everything. I feel like with your second you sort of know your way more even though it's backfiring on me now.
I do agree that he is most likely acting up for attention. It's so hard though, I don't get in from work until just before 5, then I have to get started on dinner, give them both dinner (DH normally arrives back just before dinner time or during) and then it's bedtime at 6.50 so DS maybe gets an hour with me if that once dinner time is finished in the week. I can't possibly extend that unless I push bedtime back but then me and DH don't go to bed much later than 9pm as we're always so tired.
I have considered taking the sides off DS cot especially as he has been climbing out however I can only see negatives at the moment. He'd have everything out so I'd need to get cupboard and door locks for everything. He's got a kallax unit with toys in his room, I can't see any gadgets that keep kallax boxes locked away unless we brought all new furniture. He has a stair gate on his door but I think I'd be up more putting him back in his bed. We have instead got a foam fold up mattress we lie out next to his cot so if he climbs out he's got a soft landing - this is also used for me or DH to sleep on if we end up having to go into him. He'd not constantly climbing out, I find it's only when he's had enough (so for example if he wakes up for the day whilst I'm getting ready I'll leave him in his cot a bit longer, he might climb out if he thinks I've left him too long). DD on the other hand never climbed out her cot, and even when we took the sides off she wouldn't even step out of bed without shouting one of us to get her.
TV is on and he does have access to a tablet however he rarely chooses to sit and watch for longer than a couple of minutes (which does drive me mad at times). The programmes he will watch for a couple of minutes are Paddington, fireman Sam, Thomas and an odd choice of Matilda the musical.
Regarding the HV it's nice to actually see them recommended they do much of MN seem to hate them. I've only ever had good experiences with them. The only thing I'm hesitant over is that my friend's mums best friend is on our local HV team. And whilst I completely understand confidentiality in reality would I really be able to trust her to not tell her friend. I'd never know if she did and she most likely wouldn't but I feel like it would be at the back of my mind that they might know.
When I get back from work I'm going to avoid the high chair, try my best to walk away from any tantrums or hitting, and try and give him more attention in that hour between dinner and bedtime. If this all fails I'll contact the HV.
Thanks again.