If Ariella has $200 more in her son's saving account than Daniella has, then she has $400 + $200 = $600
If she earns an interest of 10% in the first year, her savings account increases by 10/100 * $600 = $<<10/100*600=60>>60
In the second year, she earns the same amount of interest, which $60 + $60 = $<<60+60=120>>120
The total amount of money in Ariella's account after two years is $600 + $120 = $<<600+120=720>>720
#### 720