To me they are the same. The second sounds slightly more American to me.

No, there is no difference in meaning. 'Help' can be followed by either the bare infinitive ( 'wash' ) or the 'to' infinitive ('to wash'). In this sentence, it sounds more natural without the 'to'.

As Gray and Gary have said, they're both correct. Which you prefer or think is more natural just depends on what English speaking part of the world you come from.

Hi Mai! It’s good to point out these two, but there’s no difference at all. In narrative form, the first is the correct one. Though, commonly used in a spoken communication is the second. 1)I helped Mother to wash the dishes. 2)I helped Mother wash the dishes. Take Note of the uses in a sentence: I will help to (do/action word) I will help to wash the dishes. I am going to (do/action word) I am going to help wash the dishes. I helped to (do/action word) I helped to wash the dishes. I helped (Mother) to wash the dishes. Have a great one!

As Gary says, they're the same. Americans usually omit the word "to."