I have two kids - dd1 is nearly 16 and ds2 is nearly 8.
The gap has been fine. My dd is brilliant with her brother and I’ve been careful not to dump her with looking after her sibling to avoid resentment.
It has been a bit harder since dd hit teenage years as she doesn’t want to go to playgrounds or long bike rides or trampoline parks with him (although she did embrace her inner child on holiday this year and was a great playmate for her db!).
There was a period of a few years when it was very exhausting when ds was waking up at 6.30am daily and dd was wanting company until bedtime at 22:00 (she liked watching tv with me) so I had no free time at all. My dh was helpful and stepped in with dc2 to help.
But for the last 18 months or so, dd has wanted nothing to do with me at all - it is a cliche but she just wants food, lifts and favours. So I’m able to dedicate more time to ds2.
It does sometimes feel like we have two single children. The challenges of parenting them are so different due to age and probably also gender/temperament.
I don’t expect them to be “close” but they are fond of each other and have a good time together. We just had a brilliant and very active holiday which both the kids threw themselves into. We choose holidays very carefully so everyone “gets something out of it” - it helps that my ds is adventurous and resilient so he will try things a lot of 7-8 year olds maybe wouldn’t - whether that’s spicy food, or massive roller coasters, or a 20km bike ride, he is a “yes I’ll give it a go!” type of kid.
Sometimes I see two little siblings playing beautifully and my heart clenches but then I think, it’s only like having a single child - no worse.
I don’t have any expectations of them being close to each other as adults. Equally i can see them being friends, as they get on well now. I know my ds will miss my dd enormously when she goes to uni in three years time. I dread the day honestly! But he’ll be 11 and hopefully he will have his own friends and hobbies.