Working part-time needs to be in full agreement with your husband/partner. Your husband hasn't been completely on board with this for some time, by the sounds of it. It's now reached a point, where he's starting to insist that you work-full time.
However, you both need a proper conversation - his reasoning 'other families have both parents working full-time', isn't a reason, it's a statement. You 'not wanting to work full-time' equally isn't a reason not to either!
You mention you have a child/ren with SEN. There can be a vast difference between children with SEN. Some children are mild SEN, but others severe. Does your child need you to be at home?? If it's the youngest, I understand why you feel you need to be. The other two are at school all day (presumably), so you don't need to be at home.
You need to write down all the household tasks and child related tasks, and present your husband with the list. You then both need to decide how those tasks will be divided up between you. How will you manage holiday/inset days/sickness/school runs/appointments for the children. Your husband can't insist you work full-time, without knowing how the rest fits in!! Unless if course he's expecting you to work full-time and manage the bulk of the house/children!!
To me there's either resentment on his part that he's working full-time and you're not, there's money issues you aren't aware of or there's something on the horizon that he's aware and he knows you will need a full-time income. My guess, it's resentment that you aren't bringing in enough financially.
You may need to compromise - increase your hours to say 3-4 days per week.