Personally if your kids want it to do homework plus they may want to play PC games etc on it (I assume), I would go for a proper laptop rather than a tablet. A tablet is fine for internet browsing, online shopping etc and watching TV and videos on, and while you can get word and excel on them plus a little mini keyboard for typing, personally I really dislike squinting at the small screen and fat-fingers-ing on a small keyboard. A laptop has much better all round functionality IMO and is less likely to get carried around the house and dropped/smashed by careless kids!
What laptop to go for- would you mind saying (roughly) what your budget is?What I'm going to say is total anathema to true techie people but personally, I don't think there's a vast difference for your regular, everyday user between the different brands and specs of kit. DH who is really techie has bought me really high spec-d out expensive laptops as gifts in the past and while I was of course grateful TBH I didn't honesty notice much difference between them and my older, cheaper, lower spec'd laptops for my purposes which are similar to yours. I would go for a reliable brand such as Dell or Toshiba (HPs and Acer are usually a little cheaper but I have found a little pricey), then if you have some flex in your budget you could prioritise the following specs depending on your preferences (you can find information on the specs on the online listing or on online reviews, just google the make/model of laptop plus reviews will pop up):
-Processor (so does it have an 4th, 5th, 6th, 7th gen processor, usually expressed as an i4, i5 etc.) - even the oldest processors will work fine for what you want so don't panic if you can only afford an older one but newer ones will run faster and boot quicker etc.
-Screen size - if you will use it a lot for watching videos or playing games a larger screen is nicer
-Battery life - obviously the longer the battery the longer you can use it unplugged from the charger, particularly useful if you want to use it outside the house or if you like to sit on the sofa watching vids or browsing.
-Weight - obviously the lighter the easier for the DC to carry but TBH even my ancient brick of a dell is easily light enough for an 11 year old DC to carry around in an appropriate backpack or shoulder bag so not that much of a worry.
Where to buy from - pretty much anywhere online really, shop around for the best prices/discounts, just watch out for any obviously dodgy sites e.g. suspciusly cheap prices. The obvious is Amazon (personally I don't buy from them for ethical reasons but they have excellent customer service and usually offer good value for money). I've had good experiences using ebuyers before or also currys (the benefit being you can visit an actual store if you have one nearby and pick up and try the laptops). I've also bought second hand refurbished direct from dell before, you just need to keep an eye out as their stock changes regularly...
outlet.euro.dell.com/Online/InventorySearch.aspx?brandId=7&c=uk&cs=ukdfh1&l=en&s=dfh&dgc=IR&cid=296386&lid=5667687
Good luck!