Well, Queeny, you have more than one child, which make it more difficult.
I guess the first question is, do you have parents nearby to look after them for a couple of hours?
This is my week (and I earn upwards of £200.00 a week).
Monday: All day free until dh gets home at 4.30pm. Then off to a lady who looks after dogs when their owners are on holiday. I clean her, (obviously terribly filthy house) for two hours until 7pm, then return home to cooked dinner from dh.
Earnings: £12.00.
Tuesday The same as Monday.
Earnings: £12.00.
Dog lady is over-subscribed with dogs, so I look after mildly mannered little dogs for £15 per day when she needs to off-load a few.
Wednesday Clean my local pub (this is the only day when MIL has dh, for the morning). This takes two hours. From there, I walk a quarter of a mile up the road to clean a batchelor's house who works all the time. His house is immaculate, so there's very little to do apart from ironing a few shirts. Still, being conscientious, I stick it out for two hours, then go and pick up ds. I get £20.00 for 1.5 hours work.
Earnings: £32.00.
Thursday Clean pub, take DS with me. He's been coming with me since he was 3 months old, and is as happy as Larry there. Thursday Evening, back to the dog lady for two hours.
Earnings: £23.00
Friday Clean pub with ds. Rest of the day off.
Earnings: £11.00
Saturday Clean pub (without ds because dh is at home). Usually the evening off, though can often be called to work behind the bar of said pub (then earnings in excess of £30.00 per shift).
Earnings: Minimum £11.00, Maximum £41.00.
Sunday Regular night shift at pub.
Earnings: £27.50.
Disclaimer: I pay tax on some of these jobs, but not all. I don't claim any support from the government.
I guess what my very long post is trying to say is that, if you keep your eyes and ears open, and you have a couple of hours in any given day without children, you can earn money.