Are you a single parent op? If not I'm wondering if the issue is your partner/spouse isn't stepping up?!
If that's the issue I would heavily caution AGAINST going part time because if/when you split you'll be screwed!
I would recommend you look at your budget again using the Mse template, also a very good site for all kinds of money saving ideas for families
I'm also thinking your dc are quite young still if soft play is still a regular event? In which case it sounds to me like you may be overspending on their activities.
How much do they actually do weekly/at weekends and do they ever get real downtime? This is important not only for saving money but also for your AND THEIR mental health. An awful lot of kids now get stressed when they don't have plans as they've never learnt/been taught to relax - this is a hugely important skill not only imo but many child health and development experts
That said for when you/the dc are wanting to do something again the Mse site not only has lots of ideas for free/cheap things to do but is a good site for pointing you in the direction of deals and vouchers etc and eg showing you how to make the most of loyalty card points or your bank accounts options or whatever. I'm on the Facebook page too and just this week there was an article posted about getting the meerkat 2 for 1 cinema deal by purchasing £1 worth of travel insurance, also look at "season tickets" for things like soft play and cinema and similar, also when it comes to dcs birthdays and Xmas most places do gift vouchers now so rather than them getting a pile of tat why not mention to those who buy for them that eg vouchers to their favourite soft play would be super useful?
Google your nearest large towns/cities "cheap and free things to do with kids in ..." and you'll get a TON of stuff come up. When my dd was little we'd spend the holidays visiting free museums and art galleries and often the local library service has a load of activities for them from reading challenges (reading is a great down time activity) to crafts to plays put on by touring educational organisations.
At home they can do crafts, cooking, baking, colouring, puzzle books - and chores! They're never too young and it would ease your load a little
When my dd was little I had an "I'm bored" jar for if she was moany and said she was bored and I'd point her in the direction of this which contained on pieces of paper various chores, funnily enough she rarely moaned 
How much down time do you get and how much does your partner/spouse get?
Also good to get kids outdoors in the open air in all seasons. Walks, trips to beach or park etc are all perfectly valid and healthy activities. Simply invest in good warm/wet weather gear (not that little kids really care!) I have many fond memories of such days and so does dd, even when she got older and more independent she would pester her friends to go walks in the middle of winter! (Very much an outdoor cat my dd) you know that Facebook meme "that one friend that goes 'we'll walk it, it's not far' "
That's my dd!
@BarbaraofSeville is right too - review your current bills etc for unnecessary expenditure or ways you can cut back - Mse again great for this! Learn to haggle too and be a bargain hunter! Eg this time of year is usually perfect for picking up winter coats, wellies and woolies because people are wanting/buying summer stuff. Until dd was a bit more fussy teen (and it was harder to predict what her size would be!) I used to buy her good winter coat in June/July for just a few quid compared to 30/40+ in the winter. Same applies to summer stuff in winter or certainly when the shops are trying to get rid of summer to make way for winter items. Summer stuff is generally cheaper so not as big savings but it all helps
Also take care of clothes and shoes properly and they'll last you longer. I've cheap primark T shirts and jumpers I've had for about 14 years and they're still going strong! Learn to adapt/upcycle clothes too. Old jeans that have been outgrown are easily turned into shorts (I had a lanky skinny kid though) jumpers or shirts if the sleeves are past their best unpick them and make them sleeveless, light coloured items that have attracted stains (tomato based sauces are a bugger for this!) dye them a dark colour in the washing machine (you can get the products easily to do this) hell I've even not bothered buying a dye but washed light items in a dark wash with particular colours and deliberately mix washed them! Learn to fix zips and fastenings.
Same applies to home items - I'm shocked how many people don't know to check if an electrical item doesn't simply need a new fuse in the plug or will throw a lamp out because the shade is past it's best!
You could even learn to cut your and their hair. My dd hated the hairdresser when she was younger so I cut her hair I even dyed it and styled it for her. Can be a lot of fun. Boys/mens hair can be even easier with clippers
But I think the main thing is I'm not saying you personally have to do all this op, your partner/spouse and the dc should all be helping too especially partner/spouse