Now don't take this as completely gospel, but I'll give you a general rundown on things. You would need to set up a trust so that they couldn't get the house till a they reach a certain age. The trust can be managed by the solicitors (at a possible exorbitant fee), or by relatives/friends you could trust. You'd need to find a trustworthy managing agent for the property, and they'd pay the rent into the trust, who'd then pay the mortgage. The drawback to this method, is you'd need a buffer fund for the times the place is empty, and for repairs, so the kids may not get much from the rent.
Inheritance tax doesn't kick in till you're assets are worth more than £325K, so as long as house less the mortgage, is less than this figure, then they'll be okay. If you're net assets are more than this, then you'dd need spare cash to pay the IHT. And the other problems, is getting a mortgage that'll work within a trust.
If you were to give the kids the house now, you'd then have to pay a commercial rent to them on the property, but if the net worth of the house is worth more than the £325K, and you live more than 7 years, then there'd be no IHT to pay.
As you don't seem the trust the kids with their inheritance, then you really need a chat with a solicitor that's conversant with trusts, to draw up your will.
Assuming you died next week, is there enough value left in the house for them to put down a deposit on a one bed flat each, on which they'd be able to afford a mortgage, or are they in a catch 22 situation whereby they won't have enough to establish themselves, nor to keep themselves going.