Regarding giving money to the children to get around IHT, I personally think that only makes sense if you already have enough that you both could comfortably retire today. Otherwise, you have done well by your kids, they are already in a very good position if they have cars, savings, and zero debt at ages 19/20, and it would not make sense to give them loads of money now and risk having to work longer than you want to. You may have more money, but they have a lot more life ahead of them.
Regarding pension, you said that your husband is tapered out due to high earnings, but are you? Since marital assets are joint assets anyway, the best option for both of you might be to top up YOUR pension if you have room to do so.
For whatever you cannot put into ISAs or pensions over the next couple of years, I would not knock premium bonds if you are both higher rate taxpayers or additional rate taxpayers. The prize fund may only be paying 3.6% right now, but that is actually equivalent to 6.0% on a pre-tax basis (ie if a savings account pays 6%, after 40% tax you would keep only 3.6%). Listed shares may offer more, but at higher risk, while investment grade fixed income instruments probably offer about the same but require paying an advisor unless you can pick your own.
An IFA might promise a balanced portfolio that can return 6-8%, but after taxes and fees, that works out to about the same net return as premium bonds.
IFA fees take a large chunk of your annual returns. They can add value mainly if the IFA helps you to make better decisions about asset allocation and about which tax wrappers to use.