I had just DS for 11yrs. Then DTwins. So I've had an only for as long as I can remember and suddenly what seems to be 45 children.
Good and bad:
DS:
Has travelled the world. Private schools. Easy to get childcare for one, essentially did as I pleased. Only one set of everything to buy (and store). First grandchild, parents went nuts. He just slotted into life.
DTwins:
I love having them. With such an age gap I'm so lucky they turned out to be twins as it would have been akin to raising two onlys with DS11 and a baby. I love that I'll have a big family with more grandchildren, but unless DTwins have their kids pretty young, I'll probably be dead before grandchildren from them reach 10. Yes I do have a favourite and they are DTwins, but mainly because DS has SEN but as my first, had nothing to compare him too, now I see just how insanely hard he was to raise, in comparison to how easy and joyful DTwins are. I didn't know any different at the time, but now I can see he virtually broke me, and it was often getting through the day, not enjoying it. I can't believe the difference with DTwins, who technically should be twice as hard, and exhausting me now I'm ten years older. They're a dream in comparison. DS is now a teen and that toddler time is thankfully behind us. It's because of how hard he was, I thought bugger having two of these, and wondered why on earth other people put themselves through it and how they coped. I didn't realise he had SEN until he was 7. Wasn't diagnosed until 10.
But:
DTwins mean we had to buy new car. Now having to buy bigger house. Double nursery fees. Don't underestimate the constant cost. No one offers to look after two toddlers, as it's a real skill to look after twins when you've only been used to one. Nappies again. Chunky plastic crap all over the house in form of trikes and playbenches and toyboxes. Clothes. Bottles. A nursery run and a school run to juggle. Have to work on my figure for the first time, where as I pinged back after DS. Extra tickets for everything cost a blimmin fortune. Days out that would have been £30, now seem to be £100 with the extra tickets, snacks, pair of wellies and cagaoules. We'll have three universities to pay for, three weddings, three house deposits, whereas DS would have been living like little Lord Fauntleroy and set up for life if things weren't now being split three ways.
There are pros and cons. I love my big family now. I wish I'd had DTwins ten years ago. I want more now I've experienced the joy I have with DTwins, but I'd be doing it for selfish reasons, with 3 children already and my age.
My honest advice, if you're older too, is that one wonderful DD is perfect. And I'm thinking of the children, just because you can go on to have triplets at 52, doesn't mean you always should. If you have another, it might be nice. If you don't, it's not a terrible thing.
Whatever happens, be kind to yourself and enjoy your DD 