This site is really aimed at training & exercise & the nutritional needs of people involved in those activities. We may be able to help, but a lot depends on your country.
To be honest most toddlers won't need more than food & maybe a few supplements depending on the region & the personal situation of the child. First of all I'd try out different foods; fruits & veggies often work! Just find flavours the child likes & give them that. It will be hit & miss a bit a first, but you should be able to find several foods a child will eat regularly.
If you really want a general supplement we'd need to know what country you are in & maybe there is someone from that region who knows of a brand available in your country.
Sorry I couldn't offer more, but so much depend upon where you are!