Thanks for the recommendation CMotDibbler, tho' I'm not running an advert at the moment as it's getting a bit too close to Christmas 
OP (and other PPs in siilar positions), my advice is:
If it's a long term relationship, and particularly where you have children together with the current partner as well as from an earlier relationship, you should consider making Life Interest in Possession Trusts. That means that you give your property in trust to your children but on the basis that your partner/spouse can live in it undisturbed until they die or remarry. During the trust period they can if they wish move to another property, and the trust then applies to the new property.
For a shorter term relationship or where you don't have joint children, a right to reside may be better. That can be for a fixed period of two or 5 years or so, or linked to the children's ages, eg the right to reside ends when the youngest child is 21.
So far as cash assets are concerned, these will normally form part of the residuary estate and can either be paid to the partner/spouse, or again kept in a trust fund. That decision will of course depend on the needs of the surviving spouse/partner and the ages of children, as it may be impossible, practically, to ring fence those assets if that leaves a surviving partner/spouse unable to manage.
So in the OP's case, I'd recommend, at this point, a Right to Reside, and to appoint two trustees to administer the child's money on their behalf. Assuming that your child would go to live with his/her dad, then money could be released from the trust fund to help towards the child's maintenance, education etc but he wouldn't be given a blank cheque to blow as he pleased.
If you'd like any further info, feel free to post again or PM me.