overpayments or kids reg saver?

lkmc01

Hi

I have a new mortgage with nationwide on an interest rate of 4.14%. It is on a house of 85k for which we have LTV 75%, so we have put down 21250 with a mortgage of 63750.

This leave our disposable income of 200 a month which is much better than renting when it was nothing. By disposble income I mean everything after we have paid for mortgage, gas, elec.... all direct debits, food, petrol and included Christmas, annual costs such as home insurance and car insurance.

We also owe our son 2.5k which is money from his grandparents and Christmas and birthday money. He has just turned 6 years old.

I also owe my graduate overdraft about a grand.

I want to start paying my son back at 50 a month which would take 4 and a bit years.

I have already budgeted to pay back my graduate overdraft.

Shall I: -

1. Open a kids regular saver account with halifax paying 6% and pay my sons money each month at £50 into there and pay £50 as overpayments on our mortgage at costing 4.14% each month
2. Open a kids regular saver account with halifax paying 6% and pay £100 a month through (£50 a month towards the money I owe my son and £50 a month to make over overpayments on my mortgage once the account closes in a year) I could then fix my sons money or drip feed it into another kids reg saver after the year.
3. Shall I use my instant access of paying 2.89% to put my kids money in, £50 a month and pay £50 a month off my mortgage costing me 4.14%

what do you think? any other ideas?
I was thinking that using the kids reg saver for my own money too would be a good idea (option 2) as its earning 6% instead of paying 4.14%, but then I thought that option 1 would be better as I would be saving more paying overpayments in the longer run as the mortgage is based on alot more money.