Chelsea are continuing their pre-season tour after matches in Australia and Hong Kong, with fixtures against AC Milan in Indonesia and Johor Darul Ta'zim in Malaysia still to come.
Welbeck has already joined up with the squad, and Tosin said he was delighted to be reunited with someone he has known since growing up in Manchester.
"I've known Welbs for a long time, just growing up in Manchester, so it's nice to have him with us," Tosin said.
"I think we've all seen that he scores goals. He's a good striker and he's here to help. The way for him to help is by scoring goals, and I'm sure he'll do that."
Chelsea will also welcome Henderson into the squad after the midfielder completes his involvement at the FIFA World Cup with England.
Tosin believes both experienced England internationals will bring valuable leadership to a young Chelsea squad.
"They bring pure experience," he said.
"At the same time, they're winners, so they're bringing that winning mentality to the club and hopefully we'll continue that winning."
Tosin also joked that he was pleased not to be one of the oldest players in the dressing room anymore.
"It's obviously nice, no longer being the oldest. We've got some more older and experienced players in the squad. They're still young in life, so it's fine."
Mudryk has also returned to Chelsea after his suspension was lifted, allowing the winger to resume training and match action. He made his comeback from the bench against Juventus earlier this week.
Tosin said the entire squad is supporting the Ukraine international as he works towards full fitness, although he believes Mudryk's commitment means he is already ahead of schedule.
"Misha's my guy," Tosin said.
"I've kept in contact with him throughout, so it's really nice to have him back. I'm really happy for him and you can see he's just happy to be around and back in the environment."
"It's obviously going to take him some time, but we're all here to support him."
Tosin also praised Mudryk's dedication during his time away from the game.
"His work rate is unbelievable, so no doubt he's been working throughout this whole time," he said.
"I know he's been doing sessions away and I know the guys he's been working with. His work rate is phenomenal, so I'm not surprised at all."
In their opening match of the 2026/27 Premier League season, Chelsea will face Fulham on Monday, 24 August at Craven Cottage.
