Hi,
thanks for sharing! Threads asking for suggestions pop up regularly, it is rarer for people to start threads with what worked for them, and explaining why. There are so many apps and 'educational' games and toys out there, it can be hard to find the right one.
My kids are six and not quite three, and we appear to have used a similar set of apps and stuff, so I'll comment on some you mentioned.
Maths/Numeracy
Numbers: An app for phones and tablets called Dragonbox Numbers. It's an incredibly fun game where they get to play around with living numbers, combine and divide them to solve puzzles, and get a hands-on intuitive feel for what numbers mean as well as adding and subtracting.
We tried Numbers but my 6yo never got into it - too basic at the start (don't know if it changes much as you progress?) - and my 2yo doesn't like being shown, so I need to leave her to figure things out for herself, which means with Numbers that she doesn't get anywhere. Maybe when she's a bit older. I like the principle of it, but actually it's not 'hands-on' (as it's on a screen); and from what I've seen of it, the intuitive grasping of numbers and how they fit together is similar to what you achieve from playing with Lego bricks. Which IS hands-on. So, overall we're not huge fans of Numbers.
We recently got the new 'Big Numbers' (also from Dragonbox) and my 6yo loves it and has learned column addition (and practised all the simple additions like 9+5 that you do as parts of column addition) from it, without realising he was learning. A bit early though - teachers have advised us NOT to teach column addition at this stage, but it was a bit late when I realised!
My 6yo also enjoys the original Dragonbox game (algebra) but again, it's not really curriculum appropriate at this age.
General maths: Math Seeds is an online game for a wide range of ages with many different games and a clear progression path. It's also only £30 per year which is quite reasonable.
My 6yo did this, age 3-4.5 (ish) - by when he was working on Y2 material. What sets it apart from many other programmes is that it actually teaches, concepts and methods. I found that it doesn't include enough practice though (but there are plenty of sites out there to provide that!) When DS started school we stopped using it much as I found it was taking him too far ahead of the curriculum, but without him having properly mastered all the concepts.
We transferred some of the things we encountered on Maths Seeds into hands-on stuff, e.g. we made ten-frames out of egg boxes, and played a game called 'Ten Frame Towers'.
I'll look into Slice Fractions, sounds interesting, thanks.
We got the board game 'Plyt' for Christmas and DS loves it, great for practising times tables/mental arithmetic. The best part is that it's something you can do together as a family, with everybody being challenged, and yet everyone has a chance to win.
OSMO combines iPad with hands-on real stuff, and OSMO Numbers has been a success with DS. Great for practising/getting a feel of how numbers fit together, how big numbers can be made up in various ways out of smaller numbers. It is IMO very overpriced though.
In an effort to 'extend sideways' we introduced DS to chess and to coding. Dinosaur Chess is an app that teaches the basics and provides some great practice too. Often beginners are made to play against a 'weak' computer who makes silly moves/mistakes, so that they have a chance to win. But that just teaches them 'bad' chess. Instead, in Dinosaur Chess you get to play e.g. with King and 8 Pawns against King and 4 Pawns.
We have used Tynker for coding, but that's been DH's part, can't tell you much about it. Also OSMO Coding, good fun, teaches you to 'think' like a coder, plan ahead etc. and is hands-on with physical items rather than just on the screen. But at the end of the day, quite limited in the extent of what can be done/learned, and again IMO overpriced.
Reading/Literacy
I'll just mention ReadTheory here, often recommended on here by irvineoneohone. Definitely has more of a 'work' aspect to it than just games, but used it for a while with DS, as a teaching aid rather than just a 'test' (i.e. me sitting with him, explaining questions and answers), and it has done wonders for his comprehension.
Science and other stuff
Both kids enjoy GoJetters on TV and have been picking up lots of geography from that. We also have a 'cuddly' globe and an inflatable one, totally non-delicate and cheap, so they're always to hand when a place needs to be located, or something such as time zones/day and night/seasons/eclipses etc needs to be explained. A jigsaw puzzle world map comes out every now and then and is quietly helping DS remember which country is where.
With regards to history, I've found that DS enjoys a good (age appropriate) historical fiction book and so I find him ones that match the topics being covered at school. It seems to bring it to life for him.
We tend to follow the kids' interests so e.g. when DS was into dinosaurs, we read books on dinosaurs, watched videos, went to museum, started a dino figurine collection, ... and lots of chats. Resulting in him gaining lots of somewhat trivial knowledge, which was soon forgotten as his interests moved on. But also in concepts and stuff that is transferable and stayed with him (carnivore, herbivore, omnivore, ichtyophague/diurnal, nocturnal/geological ages/processes involved in fossilisation/how scientists work).