Which activities are, in your opinion, worth it?

I am the same as you, and I have basically just let Ds1 do nothing but school for his reception year as it exhausted him, and it allowed us to be free and easy and have children over for tea after school, pop into the park or the library after school etc whenever it suited us.

He is in year one now and just turned 6. This year, he has started weekly swimming lessons, a monthly cooking club and is registered for beavers. He loves cooking and is really into singing, the make up of an orchestra, the types of instruments he can hear in pieces etc. DS1 is not at all sporty, so I haven't pushed him towards that. He is also on the waiting list for music lessons, and while he waits, I will see if he is showing any leaning towards a particular instrument. The teacher teaches all sorts of instrument, which makes it easier.

There is plenty of time imo for them to join clubs and build hobbies. I didn't start anything like this until I was at least 6, and then I did dance, gymnastics, brownies etc and later on, violin and drama.

Swimming would be top of the
List
I have older teenagers now

I would be worried if they were not strong swimmers with them both going off on holidays with friends etc

Swimming here too. DS1(3.5) also does Rugbytots because its something DH can take him to on a saturday morning.

I would say at this point just pick activities you can get to easily and don't hate, give them a try for a lesson, a term, a few weeks, carry on if DC likes it, choose something else if not.

I like the Beavers idea as well when they are old enough.

swimming

I'm like you with no bias at all. I did feel swimming was essential, as much for social reasons as for safety, so apart from that I went with the DCs interests as they grew up.

I think the key thing is to check out what's on offer for any interests they do have. And let them try different things.

DS1 did football because all his friends were, but hated it. He eventually tried Tae-Kwondo and loved it.

Also look ahead, I put DSs name down for Cubs in good time or he wouldn't have got a place. Ditto DD and Rainbows.

Turned out mine are all into music, music lessons have been well worth it for us. DS 1 and DD started lessons at 8 on orchestral instruments, DS2 started piano at 6 because he was absolutely desperate.

Swimming definitely. Just purely from a safety point of view, but not necessarily just yet, although I started Ds1 on baby swimming when he was 4mo. Had to stop it when he was a year old, as he got more and more upset going - then started again when he was nearly 4.

I put DS1 into football (Little Kickers) when he was 2 3/4, because he loved football, has a useful left foot, and he needed to learn some "discipline" (listening and learning to do what he's told by other people).
I also put him into dancing when he was 3, to learn co-ordination, balance and more "discipline". He still does both of these at 6.

When he's a little older, probably 7, I'd like him to do a music lesson - his choice of piano or guitar - I'd prefer piano as it helps with using both hands effectively, but up to him.

So at least a team/group activity, and a safety activity would be my recommendation - and then music is just a nice add-on if you can afford it.

Swimming. Other things like music are nice if you can afford it but swimming is a must IMO.

I'd look at waiting lists for beavers and get him in the loop for that when he is old enough.

And swimming, as I think it's an important skill which if he enjoys could turn into a great hobby too.