i would like to know if i have to toivel my babys spoon, the top is metal and the bottom which he leaks is plastic
If the metal part comes into contact with the food, and the spoon cannot be used without it (meaning that the plastic part alone cannot function as a spoon), then it requires tevilah. If in doubt, it is best to be tovel the spoon without a berachah, or to make a berachah on other items that fully require tevilah.
Sources: See Shulchan Aruch, YD 120:6, and Rema, YD 120:7; Shach 12; Chochmas Adam 73:11; Tevilas Keilim 1:6. Where a utensil has an essential metal part that does not come into contact with food, Shulchan Aruch rules that there is no obligation of tevilah, but some of the authorities above write that there is an obligation, and it is preferable to be tovel the utensil, without a berachah. Concerning plastic utensils in general, the common custom, and the ruling of the great majority of authorities, is that tevilah is not required.