If you're serious, you could maybe start by doing the following:
offer to do it for free for the first two or three parties - eg, for mums you know well/are friends with.
when doing these, keep a tight record of costs incurred and add in your time - basically get a structure for the planning and the cost, check out your chains (eg entertainers if you use them)
get a wordpress site - basic one, for contact info, with a memorable name
get your friends you threw the first /second.third free ones for to write up good feedback/recommendations/reviews - whatever they are called
get on fb, and ask everyone you know to put the word out.
dont loss lead at first though - people then resent paying more. just do it for free to begin with, for your own research then go.
might be worth doing some research on things like insurance, if you're doing it for money, and checking those costs. you may need public liability insurance - I have no idea.