Should I let my kids visit their dad in prison?p

My kids dad is in prison. Their grandma wants to take them for a visit… My oldest loves her dad like no other (the other do too but oldest had more time with him) but I’m just nervous for them. I’ve a had a few ppl tell me there’s no way they’d let their kids do it but I’m torn. They love their dad & he was never bad to them. Any advice?