This explains the difference between inheritance tax and income tax on gifts
https://www.shepherdsfriendly.co.uk/your-resource-centre/gifting-money-to-children
SWP's Back is correct that there is no income tax liable on gifts to children, but there are limits on what gifts you can give away to avoid inheritance tax (this is where the 7 year survival rule comes in).
What isn't crystal clear to me is if I bung my daughter £20k (fat chance in case she's reading) and then pop my clogs after 5 years, bearing in mind my age (54) this would be an unexpected demise, so the 20K gift would clearly have been given in good faith and not in an attempt to avoid IHT. Even so I suspect (though I'm not sure) that this gift would then be subject to IHT