I'm low on vitamin d i'm taking vitamin 3d liquid can i still take my chewable kids multi vitamin which says has 400 iu in it on the back of bottle ?

Yes, ok: It appears liquid Vitamin D3 comes in different concentrations: one has 2000 IU vitamin D3/drop; another only 100 IU/drop,. I'm not sure how much liquid 3D you are taking. Unless you are quite deficient, the recommended daily allowance is 600 IU per day, so I would really keep your daily intake to not more 1000 IU per day total: the liquid plus the chewable.