Is it possible for a man who is raising/has full custody of his baby to get WIC or any kind of assistance ?

Yes very possible

If the mother already was on an assistance program for the child, then he needs to prove that he now has custody of the child and he needs to get that assistance transferred to him for the child. He needs to go to the WIC office and prove that the mother no longer has custody and let them know that she has kept the WIC card. It is illegal for the mother to continue using any WIC benefits if she no longer has custody of the child.

Qualifying for assistance will be based on his income. If he makes too much money, he won't qualify to continue getting assistance through WIC or any other welfare program.

It is not based on the sex of the parent caring for the child. It is based on the income level of the parent caring for the child. In most cases, men do make more money than women which is why the mother usually qualifies for programs like these and the father don't.

EDIT: I realize you don't know these things or you wouldn't be here asking. I am just giving all the basic information to put you in the right direction to try to help him get the assistance he might qualify for. Contacting the WIC office is the first step because he needs to prove he has custody so that the WIC office will cancel the card that the child's mother wouldn't give to him. (which is also illegal BTW - the mother can't just turn over the WIC card to him because, as I mentioned, qualifying for that program is based on household income and now that he has custody, he needs to apply to the program.)

No. But his children can get benefits. In that sense he can get assistance. But he himself is not eligible for benefits. Good luck! Local law will apply. Talk with a local attorney IF you can't get anywhere with the office that handles the paperwork for WIC applications. He may have to show proof of custody and/or other documents.

100% i did for my twins

I seriously doubt it! Sexism against single fathers is still alive and well and living in this miserable country!