What to do in rainy Brighton

[Starlight2022]

Visiting family in Brighton/Hove over the Easter holidays with a baby and 5 year old. Apart from the aquarium, what can we do indoors if it’s chucking it down?

The pier! My 3 year old is always happy to spend hours in there with a bucket of 2 pence pieces for those slot machines, and when my 8 month old was a baby, he just slept in his buggy oblivious to what's going on