I've tried NIDO for my little one but somehow he refuses to take it no matter how much I convince him to, what brand should I try next?

How about Bonakid? I heard it tastes good for kids. However, as far as I know it contains a significant amount of sugar, which probably explains the kids' love for it. It won't hurt to try, anyways. Of course, you can always ask your pedia for more options.