Two apps my kids have been using, with me being with them for supervision, are:
Brain School: Contains 20 different games that challenge and train the brain! Covers verbal, musical, numerical and spatial subjects. Very very fun. You graduate when you’re done!
Woozworld: For a little older kids. Helps understand trading, business and finance. You do need to supervise because there’s older kids who can log in and use bad words. Hasn’t happened with us ever but the potential is there. My daughter and her cousin in another state log in at the same time, set up a shop and sell! It’s quite fun watching the little entrepreneurs scream when they make a sale!