You have a lot organised which sounds exhausting with such young dc. It'svery hot here not sure lakes will be as bad.
I cant place where you are but maybe going between the local parks (with lovely scenery), a nice pub (with a drink) and extortionate priced bus back and an ice cream could be easier and less exhausting.
Grasmere: has a lovely little park where you can see the hills, lunch in tweedys bar and go buy delicious Grasmere gingerbread (give it as gifts, wrapped in greaseproof paper bundle your friends will thank you for) , plus a walk in the shady woods at Rydal water, babies in carriers or use the accessible path. Natalie one day just an idea of things to do.
Keswick go to Fitz Park near the leisure centre, absolutely lovely and space to run free. Good cafe the park or picnic from nearby sarnie shop. The path out to Threlkeld along the river greta starts there, buy a map in town centre it is accessible so there's always a pushchair walk from Keswick to Threlkeld and a fab meal at the pub there. Shopping in Keswick I like joules and Seasalt, you might not. There's another park, Crow Park by the lake which would be good to grab sarnie and picnic , go and feed the ducks then walk along the lake shore past the lake side theatre. You could even strike out a bit further round derwentwater to the beach. Thats at least 3 days of stuff to do. Fish and chips at the Keswickian.
Ambleside is another good one, park by the yha, get lunch at the pub by the water, take the kids to run around on the grassy park area, no play park but fun to explore, this is a less good option but good if you have a bus pass.
Coniston again has a great little park and the bluebird cafe next to the lake is lovely to eat at. Older one can dip a toe in the lake here.
Buttermere half the lake is pushchair friendly I think (check). Its national trust so could walk past the trout pub and anticlockwise eat at the Trout after.
I said yanbu to go home but it's never going to be easy holidays with 3 under 3.
You are a long way from home and I think if you ignore the planned activities which you can do anywhere in the UK you and dh could enjoy the scenery which is truly stunning. The lakes are one of the most beautiful parts of the UK.
Take the pressure off planned activities, slow it down, take in the scenery with a glass of wine or beer and at least the under 2s can be strapped in whilst you get a meal together.
Give the lakes a chance because they are fabulous.