They won't increase the amount beyond what you can afford to pay, and in any case, your payments would only go up if your circumstances actually improved.
The IP wants the IVA to succeed just as much as you do, and won't impose an unmanageable payment increase. If you feel that whatever they are proposing that you increase your payments by is unmanageable, you can always tell them why it is too high. You will certainly be allowed reasonable costs for bringing up your young child.
Having said that, you are expected to produce the best return for your creditors that you can in an IVA, so if your circumstances do improve, the IP won't want to see you spending your money on luxuries !
Philip Beck -
www.freeivaadvice.co.uk
Licensed Insolvency Practitioner and IVA specialist