Esmé has been swimming since 4 weeks. She just wears a swim nappy and a swim costume - just a normal one - nothing special. The thing to watch for is them being cold - if they are under water they will stay warm quite a while - its when they get out that they get cold.
Some of the boys in our class just wear a swim nappy and nothing else. If the water is warm enough you don;t need to splash out on anything special
Yeah depends on the pool. Sometimes my 7 month old is just in a normal swim suit and sometimes with a wee neoprene body warmer on top - like these ones from Jojo
Def agree about the tip to wrap them up and dress yourself first. Goes against what you think but its better if they get upset when you are dressing them and need a cuddle - you are dry.
I've been going swimming with Matt since he was 3 months, the pool we use is 32 degrees at a minimum. The lessons are only for 30mins as any longer and they will be too cold. The woman who runs the lessons says we need to have happy nappies over swim nappies, I can see why as they are quite snug on boys. Some of the other babies where a little vest on top, but I didn't think it was needed.