@Kath my Littlr girl is 2 and she tried her with the normal Lego and she loves them but I think they are too small. We tried the toddler ones but they were too babyish for her so she wasn’t interested.
The 4+ Lego doesn't have as many parts, but I know what you mean theres nothing inbetween
We have loads of Lego Duplo. My oldest is almost 5 and still loves it. He'd be fine with normal Lego now but can't be trusted not to leave it lying around for 2yo or upcoming newborn to get hold of so we're just sticking with the Duplo for now. Interestingly, they're actually compatible, so you can stick normal Lego and Duplo together
Lego starts from 4+ there's also Lego duplo 2+. We let our daughter play with Lego she's 4 in August and we always supervise B&M usually have some on offer