Agree with Jenf, you need a normal contract, not the short term. Only use the short term one for odd days weeks with specified end dates. For ongoing arrangements or anything over a month use the normal contract.
Include a minimum weekly charge in case they don't book any hours or the number of hours booked is less than you expected.
If you're not open 24 hours, include earliest possible start time and latest collection times they can book. I'm not registered for overnight care so have also put that parents should not book beyond their child's usual bedtime.
Include what will happen if you don't receive notification of the days/times required. Decide if that means you have had to reserve the whole week just in case and will therefore charge for the whole week or if you are not reserving anything until you have received notification/payment and therefore you are not available and minimum charge is payable.
"The parent agrees to give as much notice as possible of any days/hours of childcare needed. The parent accepts that the Childminder may decline any request for childcare and will not under any circumstances agree to bookings which would mean going over the child ratios specified on the Ofsted Registration Certificate and/or the Public Liability Insurance Policy.
The parent agrees to pay in full for all childcare booked, whether or not the child is in attendance on the day. The parent understands that there will be no refunds or reductions if the child arrives late or is collected early. The parent agrees to pay the additional fees stated below if the child arrives earlier than the agreed start time or is collected later than the agreed collection time. The parent understands that arriving late does not allow the child to remain beyond the agreed collection time."
Or, for very irregular care I would not do a contract at all. I use a booking form which parent submits with payment for each instance of childcare required.