DNA replication and combination
To explain it briefly: 

Lets take a human as example, you are diploid and you have a pair of 23 chromosomes (= total 46) and the sex chromosomes which I will exclude for this explanation. 

Your gamete is haploid and has therefore only one of the two paired chromosomes. So for every chromosome pair there are 2 possible chromosomes. So in total you have 223 possibilites to arrange chromosomes. The gamete from the sexual mating partner also has 223 possibilites to arrange chromosomes. So in total a new diploid organism has (223)x(223) possibilites. So unique. 

However, it is always the chromosomes of the parents. So yes, parents influence the children because the genetic information of the children can be found in one of the two parents. 

Furthermore you have recombination, but you already asked another question about this. So I will not expand this answer. 

There are relevant articles in Wikipedia on genetic recombination and meiosis that I would recommend.