Hi pod and welcome to the forum
If you cannot afford the IVA payments, and £300 is unlikely to be acceptable under variation proceedings, I suggest you consider bankruptcy proceedings. You have tried, and events outside of your control have led to this situation.
I can understand your disappointment at your IP's attitude, and suggest you tell them to carry on with the failure and to commence bankruptcy proceedings against you. If you own no assets, then you are unlikely to be affected duly, and it brings an end to this hassle finally.
If you feel, however, that you can make a sensible offer of variation to the Supervisor, then they are duty bound to consider this and present it to creditors. Work out what you can afford to pay now, and what you can when your wife returns to work, building in the cost of childcare.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk