Perhaps you should try some spelling variations:
thieu nien » thien nhien
hieu tieng » viet tieng, dien tieng, tiep tieng
hieu vien » hieu hien, hieu viec, nhieu viec
tu sach » thu sach, su sach, te sach
bach tu » bach thu, cach tu, bac tu
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
ca dan » cac dan, ca dao
dan vi » doan vi, don vi, dan va
vi cua » vai cua, di cua
x hoi » xa hoi, o hoi, x ho
tu ca » tu cac, tu cua, tu can

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky nang x hoi. ((((hieu vien) OR (hieu tieng))) or (thieu nien)) bach tu ca dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang x hoi. ((((hieu vien) OR (hieu tieng))) OR (thieu nien)) bach tu ca dan vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang x hoi. ((((hieu vien) OR (hieu tieng))) or (thieu nien)) bach tu ca dan vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang x hoi. ((((hieu vien) OR (hieu tieng))) or (thieu nien)) bach tu ca dan vi cua tre*.