I have Lenovos to use with work and I hate them - so slow, unreliable and temperamental. I may just have been unlucky, though.
Obviously it depends on what your budget will run to, but I'd avoid the £250-£300 ones if you're in a position to do so, as that only really covers the very basic components (such as the chassis, screen, battery, charger, Windows licence etc.) and there's very little left for quality components. I really don't think they're fit for purpose for any but the lightest occasional user. If you can stretch to £500-£600, you'll get something much faster, more responsive and more reliable that will last considerably longer. Also, bear in mind that a large percentage of the cost is the Office (Excel and Word etc.) software (not to be confused with the Windows operating system). Check if this is included, as it often used to be by default but now frequently is not. You can use free alternatives (which may or may not be compatible with school work and other programs), or go for the subscription model (Microsoft 365); but if you prefer a one-off purchase of Office software, it lasts the life of the device, so you'll have to buy it all over again if/when it fails or you want to upgrade.
You may prefer the peace of mind of brand new, but personally, if I only had/wanted to spend £200-£300, I'd go for a refurbished ex-business model of a decent spec from a reputable retailer over a new one.
I definitely second getting at least 8GB of RAM and I would suggest getting one with an SSD (solid-state drive) only and without a HDD (hard-disk drive) - SSDs are faster and less likely to fail than HDDs as they have no moving parts. HDDs offer more storage for less money, but they can be the weak link (and are noisier and consume more power), plus a lot of things are cloud-based nowadays, so if you can get a SSD of 250GB (some will be taken up by Windows and other rudimentary software), that would likely do you fine. You can always get huge-capacity USB flash drives very cheaply these days if they have a load of big files, photos or videos they want to access.
I don't know how old your kids are, but I would also plan ahead for them getting older, hence the recommendation for a better spec model. I chose a decent-ish spec one for my 6yo DS (refurb from eBay was all we could afford - a Dell, which is one of the better branded ones IMHO), which was more than plenty sufficient for what he needed then, but he's now 8, has really taken to it and knows more than I do learned a great deal, and whilst it's still going strong, I'm now seeing that it is more limited in relation to his current abilities and what he wants to do with it.
Apologies if any of what I've said is blatantly obvious to you - we're all at different stages, so I'd rather mention something that you already know full well than not mention what you may not have previously had chance to encounter!