Tom Kaulitz: All the information you need to know about Heidi Klum's spouse

Following his marriage to Klum

Kaulitz took on the role of stepfather to her four children

 Henry and Johan, and daughters Leni and Lou

Kaulitz "made a huge effort to get to know

the moment he met the children, a source told PEOPLE

he now views himself as a "extra dad" to them.

he now views himself as a "extra dad" to them.

"He participates in activities that the girls like and plays sports with Heidi's boys.