I think we should have VAT on basically everything. That's how the Nordic countries do it, more or less - flat high rate of VAT on pretty much everything, and then there is more money to fund a better public sector, including more generous benefits for those who need them.
If you want to "help poor people," then the Nordic way (VAT on everything, then more generous benefits) makes more sense than "Oh, let's take VAT off kids' clothes in case poor people struggle."
I know that these VAT exemptions seem "kind" in an emotional kind of way, because we all picture a scene of "a poor person buying kids' clothes and struggling" in our minds when we think about this. But rich people buy loads more kids' clothes than poor people (who "make do," use handmedowns, get second hand clothing as much as possible), so most of the benefits of no-VAT-on-kids-clothes goes to well-off people.
Putting the VAT on kids' clothes (and all the other things) and then having more generous benefits is a much, much more efficient and effective way of helping those on low-incomes.
In addition, the timewasting, complication and ridiculous workarounds which are created by the UK's complex and illogical mess of VAT exemptions is economically inefficient and harms growth and productivity. Businesses waste time and energy fighting their way through all the red tape and silly rules instead of on other activities that they should be focusing on.