This depends so much on circumstances and the age and behaviour of the kids though, doesn't it?
I wouldn't take my three kids alone to soft play, no.
Firstly, I don't drive. The nearest soft play accessible via public transport is around a 45 mins 🚐 ride away and it only comes every hour. So I wouldn't want to risk missing one/one not showing up and being stuck for two hours at the other end. I would possibly consider it only with the eldest who is 6 and could be trusted to sit in a cafe in the shopping centre or look round the shops whilst we waited. No way with the three year old, and no way with the 2 month old because they could decide they want breastfeeding right when we need to leave for the bus, or shit all up their back at that exact moment or something. Plus if I couldn't get on the bus with the pram - its a very tiny bus that does that route, not a normal sized bus, so there's only space for one pram or wheelchair - then again I wouldn't want to be trapped for a further hour in the hope I could get the next bus.
Add to that my 3 and 6 yr old do not play well/independently in soft play and I can't be running around a play frame with a 2 month old. The 3 year old also would probably eventually start trying to mess with plug sockets, or run out, or mess with stuff on tables and whatnot which would be not fun and difficult to deal with what breastfeeding the 2 month old. Then if any of them need the toilet or baby needs a nappy change I'd have to take all of them with me into small, dirty soft play toilets.
No thanks.
Obviously as they age things will change but right now it's definitely not something I'd want to do.
I actually don't find the odd day at home too bad with them because my 3 and 6 year old do generally play together pretty well without too much bother. And the 2 mo is a pretty easy baby so far.