One possible version:
Dear Sir/Madam,
I am writing to interested in the accommodation you have offered to someone to help with two children. I am a twenty one-year-old boy and I come from China. I have been learning English for several years and besides it, I can also speak two other languages fluently which are Spanish and French. I once worked in a kindergarten for one year, so I know how to take good care of children.
I am enquiring about the time which I should help you with the children and for how long. Moreover you have mentioned languages, but we do not know what languages are requested. I would like to ask about the experience what kind of experience, teaching or looking after children. Lastly, I am asking about the accommodation what kind of it and how it is like. I look forward to receiving your letter.
Yours faithfully,
Li Hua

略

One possible version:
Dear Sir/Madam,
I am writing to interested in the accommodation you have offered to someone to help with two children. I am a twenty one-year-old boy and I come from China. I have been learning English for several years and besides it, I can also speak two other languages fluently which are Spanish and French. I once worked in a kindergarten for one year, so I know how to take good care of children.
I am enquiring about the time which I should help you with the children and for how long. Moreover you have mentioned languages, but we do not know what languages are requested. I would like to ask about the experience what kind of experience, teaching or looking after children. Lastly, I am asking about the accommodation what kind of it and how it is like. I look forward to receiving your letter.
Yours faithfully,
Li Hua

略