Is it worth watching another kid when you have your own and only getting 160 a week?

My boyfriend wants me to watch his friend's son for 10 hours a day and 5 days a week and for 160 a week.I remember paying about that much 5 years ago for daycare and for only 8 hours a day.I know that it's almost 800 a month when it's low income,but you only pay a quarter of that if you are low income and paying child care subsidy.I also have a 2 year old,and his friend's son is 3 years old.Not potty trained yet,and I think of my sanity,because that's two little ones and thay can get really rowdy sometimes.I just feel like it's not really worth it.Can anyone give any kind of advice?