which visa should i apply for china

hii..my husband is working in shanghai from last two month.I want to visit there in dec.for 1 month and again in may for 2 month.I have two son.elder one is 11 yrs and younger one is 3+ yrs old..they also go with me .please suggest me which type I should apply..thanx a lot for ur kind words.please reply me as soon as possible